• Nov 30, 2024
  • By Millie Jones
  • 0 comments

Kids’ Mattress Size Guide (Millie & Jones Edition)

Choosing the Perfect Children’s Mattress for Healthy Sleep and Growing Bodies

Choosing the right kids’ mattress size and type is one of the most important decisions you can make for your child’s comfort, health, and development. A comfortable and supportive mattress ensures your child enjoys a good night's sleep, which is essential for their child's development and overall well-being. As children grow, the support they need from a mattress changes, from firm and safe cot mattresses to medium firm mattresses for active kids and growing teens.

At Millie & Jones, we specialise in children’s and teenage beds, so this guide has been designed to help you confidently choose the best childrens mattress size, firmness, and material, while also highlighting the best models in our own carefully curated range.

⭐ Why Mattress Size & Support Matter for Children

A well-fitted, supportive mattress helps with:

  • Proper spinal alignment and great support for the child's body

  • Healthy physical development and posture

  • Reduced nighttime waking and restful sleep

  • Better temperature regulation with breathable materials

  • Comfort for growing bones and joints, including pressure points

A mattress that is too soft, too deep, or poor quality can cause discomfort, overheating, or unsafe sleep conditions - especially for younger children. Choosing a medium firm mattress or a firmer mattress for younger kids can help prevent child rolling and ensure safety.

📏 UK Kids’ Mattress Sizes Explained

Below is a complete breakdown of mattress sizes commonly used for babies, toddlers, children, and teens in the UK.

Mattress Size

Dimensions (cm)

Dimensions (ft)

Best For

Cot Mattress

60 x 120

2ft x 3ft9

Newborns, infants

Toddler Mattress

70 x 140

2ft3 x 4ft6

Ages 2–5

Small Single

75 x 190

2ft6 x 6ft3

Young children, compact rooms

Single

90 x 190

3ft x 6ft3

Kids 4+, teens, bunk beds

European Single

90 x 200

3ft x 6ft6

Taller kids & teens

Small Double

120 x 190

4ft x 6ft3

Teens or solo sleepers

Double

135 x 190

4ft6 x 6ft3

Teens with large rooms

🧸 Cot Bed & Toddler Mattress Guide

⭐ Cot Bed Mattress (60 x 120cm)

  • Suitable for newborns to ~3 years

  • Must be firm, supportive & breathable for safe sleep

  • Should fit the cot snugly with no gaps

Look for:

  • Removable and washable covers

  • Hypoallergenic materials to reduce allergies and dust mites

  • Waterproof protection for bed wetting

  • Firm support foam made from high quality materials

⭐ Toddler Mattress (70 x 140cm)

Perfect for ages 2-5, when children begin moving more and require edge-to-edge support.

A toddler mattress should be:

  • Supportive mattress (firmer is better)

  • Durable and made with natural latex or foam layers

  • Breathable and cool with temperature regulating fabrics

  • Hypoallergenic and naturally resistant to dust mites

At Millie & Jones, toddler beds pair beautifully with ComfortSleep 15 (if available in toddler size), a firm and affordable foam mattress built for young children.

👧 Small Single & Single Mattresses for Kids (75/90 x 190cm)

⭐ Small Single Mattress (75 x 190cm)

Ideal for:

  • Small bedrooms and kids beds

  • Younger kids

  • Cabin beds & some bunk beds

Small single mattresses help maximise space while still giving children room to grow.

⭐ Single Mattress (90 x 190cm)

This is the most common kids’ mattress size and works for ages 4 through teenage years.

Perfect for:

  • Single bed frames

  • Bunk beds (with recommended max depth)

  • Mid & high sleepers

  • Day beds

Choose a mattress with a reinforced edge for durability and safety, especially for child rolling prevention.

🧭 Safety Tip: Mattress Depth for Bunk Beds & High Sleepers

  • Max depth: 15cm for top bunks & top tiers of mid/high sleepers

  • This keeps the mattress below guardrails, preventing roll-out accidents and child rolling

Your best Millie & Jones bunk-safe mattresses:

All 15cm models are bunk-safe, child-safe, breathable, and most include washable covers.

🛏️ Mattresses for Teens: What to Look For

Teenagers experience rapid growth and often need more:

  • Proper spinal alignment

  • Pressure relief at key pressure points

  • Breathability with temperature regulating fabrics

  • Durability and high quality materials

Recommended sizes:

Best Millie & Jones mattresses for teens:

  • MemoryTeen 18 → Designed specifically for teenage support with medium firm tension

  • PocketRest 15 → Great for slimmer frames or loft beds

  • MemorySupport 25 (adult-level support)

  • NaturalLoft 27 → For teens who run hot at night with breathable materials

🔍 Choosing the Right Kids’ Mattress Type

Here are the most common mattress materials for children — and how they compare.

⭐ Pocket Spring Mattresses (e.g., PocketRest 15)

Best for:

  • Proper spinal support and all the support growing children need

  • Kids who toss and turn or have active sleep patterns

  • Long-term durability and great quality mattress

Individually wrapped springs = better support & airflow to keep your child cool.

⭐ Memory Foam Mattresses (e.g., MemoryDream 15, MemoryTeen 18)

Benefits:

  • Amazing pressure relief and comfortable night's sleep

  • Cosy, hugging feel with foam layers

  • Great for kids who like a soft mattress feel

Choose breathable versions only - all Millie & Jones memory foams are cooling and hypoallergenic.

⭐ Orthopaedic Mattresses (e.g., Guardian Orthopaedic 15)

Great for:

  • Older children needing firmer support

  • Kids who prefer a firmer surface for proper spinal alignment

  • Posture support and medium firm tension

⭐ Hybrid Mattresses

(Pocket springs + foam)
Great for:

  • Growing teens

  • Combination sleepers

  • Long-term comfort with all the support and breathable materials

⭐ Reflex Foam (e.g., ComfortSleep 15)

Best for:

  • Younger children

  • Budget-friendly yet supportive mattress

  • Lighter body weights

Offers firmness and structure but without the heat retention of older foams.

🌡️ Temperature Regulation for Kids

Children sleep hotter than adults.
Look for mattresses with:

  • Airflow layers and breathable materials

  • Pocket springs (naturally cooler)

  • Moisture-wicking fabrics and temperature regulating covers

If your child sweats at night → choose PocketRest 15 or NaturalLoft 27.

🧼 Caring for Your Child’s Mattress

To extend mattress lifespan:

  • Use a washable mattress protector or mattress cover

  • Choose waterproof layers for toddlers prone to bed wetting

  • Rotate the mattress every 3-6 months

  • Check for dips or sagging annually

  • Replace every 7-10 years, or sooner if outgrown

All Millie & Jones mattresses arrive vacuum packed for easy setup.

❓ FAQ

How often should I replace a kids’ mattress?

Every 7–10 years, or sooner if the child has outgrown the size or the mattress shows signs of wear.

What firmness is best?

  • Younger kids → firmer mattress

  • Older kids/teens → medium or medium firm tension

  • Bunk beds → always 15cm maximum depth

Are memory foam mattresses safe for kids?

Yes - from ages 4+, provided they are breathable and supportive (like MemoryDream 15 & MemoryTeen 18).

What mattress is best for bunk beds?

Anything 15cm deep and breathable, such as:

  • PocketRest 15

  • MemoryDream 15

  • Guardian Orthopaedic 15

  • ComfortSleep 15

🎉 Conclusion: The Right Mattress Helps Kids Grow, Sleep & Thrive

A great support mattress starts with the right mattress size, firmness, and material. Whether your child is moving into their first toddler bed, upgrading to a bunk bed, or a teen needing more support, Millie & Jones offers a mattress designed for every stage of growth.

⭐ Best for Kids (4–10):

  • PocketRest 15

  • ComfortSleep 15

  • MemoryDream 15

⭐ Best for Teens (11–18):

  • MemoryTeen 18

  • PocketRest 15 (for bunks/high sleepers)

  • MemorySupport 25 (adult-level support)

⭐ Best for Budget:

  • ComfortSleep 15

⭐ Best for Long-Term Growing Comfort:

  • MemoryTeen 18

Explore our full range of kids’ mattresses today and find the perfect mattress for your child’s bed to ensure a comfortable night's sleep and support their healthy growth and development.

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