Mattress Online Rock Hard Ultra Firm Single Mattress
The Rock Hard Ultra Firm from Mattress Online is an all-foam orthopaedic mattress rated extra firm, which means very little sink and a sleeping surface that keeps you on top of the bed rather than in it.
- Very firm, no sinking feel
- Moulds to ease pressure points
- 100-night trial
£279
Get the lowest price we've found
Save with the previous model
Some retailers still sell the earlier version of this mattress for less than the current model's best price.
Mattress Online Rock Hard Ultra Firm Mattress
More available sizes
Mattress details
Mattress
Mattress Online Rock Hard Ultra Firm Mattress
Size
Firmness
Firm
Construction
Foam
Orthopaedic
Depth (cm)
25
Layers
3
Layer Details
Reflex Foam
A flexible reflex foam layer sits at the top, which means responsive support that helps keep your spine aligned. It has a little give, but this is not a plush comfort layer.
Ortho PU Foam
The ortho PU foam core provides the extra-firm support this mattress is built around. It moulds to your shape to reduce pressure points and encourage better posture.
Reflex Foam
A second reflex foam layer at the base promotes spinal alignment from underneath. It moulds slightly to your body for a more personalised feel.
Layer details from mattressonline.co.uk product page, September 2026.
Key benefits
- Fits where other beds won't: At 90cm wide, the UK single leaves floor space free in a compact room, a loft conversion under the slope, or a child's room already crowded with a desk and wardrobe.
- Extra firm support for one: The ortho PU foam core keeps a solo sleeper on top of the bed rather than sinking in, which suits back sleepers who ache on softer surfaces.
- A sensible spare room choice: In a study that doubles as guest space, a UK single keeps the room usable during the week and the extra firm surface stays supportive for occasional visitors.
- Works in pairs: Two UK singles fit a guest room or siblings sharing, with a walkway between them, where one larger bed would swallow the floor.
- Cheap, easy bedding: Standard single sheets and a 135 x 200cm single duvet fit, and both are the most widely stocked and least expensive bedding of any UK size.
This size suits you if...
You sleep alone, prefer a genuinely firm surface, and want the smallest standard adult size; you're kitting out a spare room or student flat where the frame is a UK single already; or you're buying for a teenager who sleeps on their back and finds softer mattresses uncomfortable. Allow at least 2.1m x 2.8m of floor space and it will sit happily in most rooms.
Consider another size if...
You share the bed, or you're a broad-shouldered adult who finds 90cm restricts how you turn. We'd recommend the UK double instead: it's 45cm wider at the same length, gives 67.5cm each for two sharing, and needs a room of at least 2.6m x 2.8m.
Similar Mattresses in This Price Range
Did you know? On Mattress Unboxed we have over 1,000 different mattresses to suit all types of sleepers. View all mattresses.
FAQ's
Will the Rock Hard Ultra Firm UK single fit a bunk or mid sleeper frame?
The 90 x 190cm footprint matches standard UK bunk and mid sleeper frames. The thing to check is depth: this mattress is 25cm deep, and raised frames often specify a maximum mattress depth so the guardrail stays high enough. Measure your frame's guardrail and check its stated limit before buying.
Is the Rock Hard Ultra Firm in a UK single suitable for a child?
Be cautious here. This is an extra firm mattress, and lighter sleepers tend to find that kind of surface too unyielding, because there isn't enough give at the shoulder and hip to keep the spine level. For most children we'd suggest something with more cushioning, unless a firm bed has been specifically advised.
What room size do I need for a UK single mattress?
We suggest allowing at least 2.1m x 2.8m of floor space, which is our own guidance rather than the manufacturer's. That leaves enough room to walk round the bed and open drawers or wardrobe doors. In a child's room competing with toy storage and a desk, the UK single is the size that makes everything fit.
How much bigger is a UK double than this UK single?
The UK single is 45cm narrower than the UK double, and the two are the same length. The UK double gives 67.5cm each for two sharing, and we suggest a room of at least 2.6m x 2.8m for it. If you sleep alone, that extra width is a luxury rather than a necessity.
Can I use two UK singles instead of one bigger bed in a guest room?
Yes, and it's often the more flexible choice. Two UK singles let guests sleep separately, suit siblings sharing a room, and can be arranged to leave a proper walkway. Since this mattress is extra firm, it works well for occasional guest use, where a surface that holds its shape matters more than plushness.