Mattress Online Rock Hard Super Firm Foam Small Double Mattress
The Rock Hard Super Firm Foam Mattress from Mattress Online does exactly what the name suggests.
- Very firm, full-height foam build
- Helps keep your spine aligned
- 100-night trial & 10-year guarantee
£334
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Mattress Online Rock Hard Super Firm Foam Mattress
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Mattress details
Mattress
Mattress Online Rock Hard Super Firm Foam Mattress
Size
Firmness
Firm
Construction
Foam
Orthopaedic
Depth (cm)
23
Layers
Layer Details
Reflex Foam
A supportive foam that moulds to your body, which means it promotes spinal alignment and a slightly personalised feel despite the very firm surface. It's durable and resilient, holding its shape for an extended period of time.
Layer details from mattressonline.co.uk product page, September 2026.
Key benefits
- Genuine stretching room for one: At 30cm wider than the UK single, this size lets a solo sleeper move freely without stepping up to a full double frame.
- Extra-firm support in a compact footprint: You get the same super firm reflex foam feel as the larger sizes, in a width that suits box rooms and studio flats.
- Stable to the edges when you spread out: The very firm, solid surface means the extra width is all usable, with no sink-in soft zones pushing you back to the middle.
- Easier to manage than the bigger sizes: This mattress is heavy for its type, so the UK small double is a little more practical to rotate than the UK king or UK super king.
- A sensible guest room choice: Couples can share it for the occasional night, and firm-mattress guests are catered for without giving the room over to a bigger bed.
This size suits you if...
You sleep alone, want a very firm surface, and have outgrown a UK single but can't spare the floor space a UK double needs. It also fits if you're furnishing a small second bedroom or holiday let where guests share only occasionally, or a loft room where a wider bed would leave no standing room beside it.
Consider another size if...
You share the bed every night, because a very firm mattress gives you no soft middle to drift into and the width is tight for two. We'd recommend the UK double instead, which gives 67.5cm each and needs a room of at least 2.6m x 2.8m.
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FAQ's
How big is the Rock Hard mattress in a UK small double?
It measures 120 x 190cm, which is 4ft x 6ft 3in. That's 30cm wider than the UK single and the same length, so a taller sleeper gains no extra legroom by choosing it, only width. We suggest a room of at least 2.4m x 2.8m to leave walking space around the bed.
Is a small double Rock Hard mattress big enough for a couple?
For occasional nights, yes. For every night, it's a squeeze, and the super firm surface makes it feel more so: neither of you sinks in, so you notice the shared width more than you would on a softer bed. Couples sharing nightly would do better with the UK double, which gives 67.5cm each.
Will the small double fit in a box room or loft conversion?
Usually, and that's the point of this size. It's 15cm narrower than the UK double, which is often the difference between a door that clears and one that doesn't, or between having standing room beside the bed and not. Measure your usable floor, then allow at least 2.4m x 2.8m.
Is this size easy to move or rotate?
Easier than the larger sizes, though still a two-person job. Reflex foam at this depth is heavy and doesn't fold or flex much, so the UK small double's narrower footprint helps on stairs and in tight landings, particularly in loft rooms. Solo sleepers should still plan for help when rotating it.
Does the small double feel as firm as the bigger sizes?
Yes. The 23cm reflex foam build and Extra Firm rating are identical across every size, so you're choosing footprint, never feel. What the UK small double changes is how the firmness works for you: a solo sleeper gets a wide, uniformly solid surface with no soft edges, which suits sprawlers who need serious support.