Mattress Online Rock Hard Ultra Firm Mattress
Mattress
Mattress Online Rock Hard Ultra Firm Mattress
Size
Firmness
Firm
Construction
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.
- Room for two, space for the room: At 135cm wide the UK double fits comfortably where a UK king would dominate, usually leaving space for bedside tables on both sides.
- A firm surface that stays put: Very little sink means neither sleeper rolls towards the other, which matters more on a double where you share 67.5cm each.
- Modest room requirement: We suggest allowing at least 2.6m x 2.8m, which most UK second bedrooms and older terrace rooms can manage.
- Easy to dress: Standard double sheets and a 200 x 200cm double duvet are stocked everywhere, so replacing bedding is cheap and simple.
- Familiar size for guests: For a guest room hosting visiting couples, 4ft 6in x 6ft 3in is the size most people already sleep on at home.
This size suits you if...
You share the bed every night and your bedroom sits around the typical UK size, where a UK king would crowd out wardrobes and drawers. It also suits you if you both prefer a properly firm surface, or you sleep alone, perhaps with a dog or cat claiming a corner, and want more width than a UK single without a bigger frame.
Consider another size if...
You share every night and find 67.5cm each a little tight, and your room allows at least 2.7m x 2.9m. In that case we'd recommend the UK king instead: it is 15cm wider and 10cm longer, giving 7.5cm more each.
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Is the Rock Hard Ultra Firm UK double big enough for a couple?
Yes, for most couples. The UK double gives 67.5cm each for two people sharing, and because this is an extra firm all-foam build with very little sink, you tend to stay in your own space rather than rolling together. Larger sleepers, or restless ones, may prefer the extra width of the UK king.
What room size does the Rock Hard Ultra Firm UK double need?
We suggest allowing at least 2.6m x 2.8m for the 135 x 190cm footprint. That leaves enough space to walk round the bed and open drawers. If you want bedside tables on both sides, a slightly larger room makes daily life noticeably easier, though the minimum still works.
Should I buy this mattress in a UK double or size up to the UK king?
It comes down to your room. The UK double is 15cm narrower and 10cm shorter than the UK king, and the UK king gives 7.5cm more width each for two sharing. If your bedroom allows at least 2.7m x 2.9m and you share every night, the UK king is the more comfortable long-term buy.
Will the UK double fit up narrow stairs in an older house?
The UK double measures 4ft 6in x 6ft 3in, and at 25cm deep it is a substantial item to carry. Before ordering, measure your stairwell, any turns, and the landing, especially in older terraces or tight new build layouts. All-foam mattresses have some flex, but the box or wrapped roll still needs clear access.
Is the UK double a good choice for a guest room?
On size, yes: it comfortably sleeps visiting couples and is the format most guests know. One caution, though: this mattress is extra firm, and firmness divides opinion more than any other quality in a bed. If your guests vary widely in build and preference, a more middle-of-the-road firm mattress may please more of them.