A 2027 Guide to Choosing the Right Kids Mattress Size as Your Child Grows
Children don't need a new mattress every year, but they do need one that's right for the stage they're at. From a cot to a first bed to a teenager's room, the size, depth and feel of the mattress all change as they grow - and it’s normal for parents to be confused about what to replace and when.
This guide takes you through each stage, with the sizes to look for and the Simba mattress we'd suggest at each one.
Babies And Toddlers: The Cot Bed
A baby needs a firm, flat sleeping surface, and that's the single most important thing at this stage. Our Hybrid® Cot Bed Mattress is double-sided for exactly this reason. The firmer Baby side gives newborns and babies under 12 months the flat support they need. After their first birthday, you flip it over to the softer Toddler side, which has Aerocoil® microsprings for cushioned, edge-to-edge support as they start to wriggle, play and stand up in bed.
It's 10cm deep, it conforms to BS EN 16890, and it has a water-resistant inner cover with a machine-washable outer cover. One mattress sees your child from birth to around three years old.
From Three Upwards: The First Big Bed
Around the age of three, most children move into a single bed. This is where the bed itself matters as much as the mattress, because if they're going into a bunk or cabin bed, safety regulations limit how deep the mattress can be.
Our Hybrid® Kids Mattress is a UK single with a shallower 16cm depth for that reason, and it's the one we'd recommend for any raised bed. It has five layers, including our Aerocoil® microsprings and Simbatex® foam, so it gives real support and cushioning. Bunk and cabin beds aren't suitable for children under three, so this is the stage to make the move.
If your child is going into a standard single bed frame, any of our Hybrid® mattresses will work in a single size.
Growing Children: Room to Stretch
By eight or nine, many children are tall enough that a single starts to feel snug, and this is when it's worth thinking about the next size up. A small double, at 120 x 190cm, gives them 30cm more width than a single in the same length, which is enough room for a growing body without taking over the bedroom. If you have the space, a standard double at 135 x 190cm is a bed they'll never outgrow.
Most of our Hybrid® mattresses come in both sizes, and they're all designed to feel medium-firm, so the choice comes down to your budget and how much cooling you'd like. The Hybrid® Essential is our most wallet-friendly, and the original Hybrid® adds an extra layer of comfort and is 25cm deep.
Teenagers: A Bed For The Next Decade
Teenagers sleep like adults, and often more. A mattress bought at 14 could last them well into their twenties, so it’s worth choosing one that’s built to last. Every new Simba mattress comes with a 10-year guarantee (excluding our cot mattress, which comes with a 2-year guarantee).
A double or small double Hybrid® Pro offers additional comfort layers, including two layers of Aercoil® microsprings that respond individually to provide more tailored support as teenagers grow.
Teenage bedrooms can get warm, so the cooling features in our range are a real plus. Simbatex® foam has over five times more airflow than memory foam in independent testing*, while the Hybrid® Pro combines a breathable wool layer, graphite-infused foam, and a cool-touch Stratos® cover to help regulate temperature.
For additional cooling, HeatRelease™ is available as an optional upgrade. Its graphite strips absorb excess body heat and draw warmth away from the sleeper, helping them maintain a comfortable sleeping temperature throughout the night. In controlled laboratory testing, the upper foam layer of a Hybrid® Ultra mattress was up to 4.4°C cooler with HeatRelease™ than without.
*Independent tests conducted by Intertek in May 2025 evaluated single pieces of foam against nine leading memory foams from the top three UK manufacturers. The testing followed ISO 7231 Method B (Determination of Air Flow value at constant pressure drop) to verify that Simbatex® delivers over 5 times more airflow than standard memory foam.
A Size Chart For Quick Reference
Stage |
Size |
Dimensions |
Suggested mattress |
|---|---|---|---|
|
Birth to 3 |
Cot bed |
Standard cot bed |
Hybrid® Cot Bed Mattress |
|
3 upwards |
Single |
90 x 190cm |
Hybrid® Kids Mattress |
|
Growing children |
Small double |
120 x 190cm |
Hybrid® |
|
Teenagers |
Double |
135 x 190cm |
Hybrid® Pro |
The Bed That Grows With Them
Choosing a bed frame that will last several stages saves you buying twice. A double frame with storage suits a child from around eight through to leaving home, and the drawers or Ottoman compartment are useful for toys now and clothes later. You'll find a bed to grow into from our collection, in Single, Double, King and Super King, with upholstered, wooden and metal designs.
A Few Safety and Care Notes
- Keep a cot bed mattress flat until it's needed, and store it flat.
- Never use a deeper mattress than the bed's maximum on a bunk or cabin bed.
- Use a waterproof mattress protector at every stage. Our TripleShield protectors are machine washable.
- Rotate a Hybrid® mattress once a month for the first three months, and then every three months.
- Our foams are CertiPUR® verified, which means they're free from heavy metals such as mercury and lead.
FAQs
Yes. It's a UK single with the same Aerocoil® and Simbatex® technology as our other mattresses, so it's comfortable for an adult reading a bedtime story or an occasional overnight guest.
Our cot bed comes with a 30 day return period. Like our other mattresses, the cot bed mattress is designed to be kept flat, so store it that way until your baby is ready for it.
Flip it to the Toddler side when your child turns one. There are Firmer and Softer labels on each side so you'll always know which way round to have it.
Our Hybrid® Kids Mattress is a UK single. We don't currently stock a bunk bed safe mattress in a EU single size.
Usually not. A Simba mattress gives them the cushioning and support they need on its own. A topper is useful later, for a teenager who'd like extra comfort on a mattress they already have.
