Jay-Be Flex Ultra Firm King Size Mattress
The Jay-Be Flex Ultra Firm is a hybrid mattress built for people who want a genuinely hard sleeping surface.
- Extra-firm, traditional sprung feel
- Breathable fibres reduce heat build-up
- Hypoallergenic, vegan-friendly fillings
£321.69
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.
Jay-Be Flex Ultra Firm Mattress
More available sizes
Mattress details
Mattress
Jay-Be Flex Ultra Firm Mattress
Size
Firmness
Firm
Construction
Foam
Hybrid
Rolled
Open Coil Spring
Depth (cm)
21
Layers
4
Layer Details
Advance e-Fibre
A breathable filling layer at the top of the mattress. It lets air move through the surface, which means less heat building up around you overnight.
Rebound e-Fibre
A second breathable filling layer beneath the surface. It sits between you and the springs, adding a little resilience without softening the extra firm feel.
High Density e-Fibre
A denser breathable filling layer above the spring core. This is where much of the firmness comes from, giving the surface its solid, supportive character.
Open coil spring core
A sprung core providing reliable support across the mattress, with 325 springs in the king size. Open coil systems move as one unit, which means a firmer, more traditional feel than pocket springs.
Layer details from furniturevillage.co.uk product page, September 2026.
Key benefits
- Real space for two: At 150 x 200cm you get 75cm each for two people sharing, enough to change position without negotiating for territory.
- Length for taller sleepers: The 200cm length is 10cm more than a UK double, so a partner over six foot stops sleeping diagonally or hanging feet off the end.
- 325 springs in this size: The king carries 325 open coil springs, giving that solid, traditional firmness edge to edge across the wider surface.
- Breathable across a big surface: Three e-Fibre layers let air move through the mattress, which means less heat pooling between two bodies sharing the bed.
- Slim profile, easier handling: At 21cm deep it's slimmer than many hybrids, which makes turning and moving a king-sized mattress noticeably less of a struggle.
This size suits you if...
You share the bed every night and a UK double has started to feel like a compromise, you both prefer sleeping on top of the mattress rather than sinking into it, or one of you is tall enough that the extra 10cm of length over a UK double is the real reason you're upgrading.
Consider another size if...
Your bedroom is smaller than the 2.7m x 2.9m we suggest for a UK king. The UK double would suit you better, and it needs slightly less room: we suggest at least 2.6m x 2.8m for that size.
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
What size room do I need for a UK king Jay-Be Flex Ultra Firm?
We suggest a room of at least 2.7m x 2.9m for a UK king, with 3.2m x 3.2m feeling comfortable once wardrobes and bedside tables are in. That's our guidance rather than Jay-Be's. New build master bedrooms can be tighter than they first appear, so measure with furniture in place before committing.
Is the Jay-Be Flex Ultra Firm UK king big enough for a couple?
Yes, comfortably. The UK king gives 75cm each for two people sharing, which is 15cm more overall width than a UK double. On an extra firm surface like this you sleep on top of the mattress rather than rolling towards the middle, so each of you keeps to your own side more naturally.
Will the UK king suit a sleeper over six foot?
The UK king is 200cm long, which is 5ft x 6ft 6in in imperial terms, and 10cm longer than a UK double. For anyone approaching or past six foot, that extra length usually matters more than the width. Feet stay on the mattress rather than pressing against the footboard.
Does the open coil core disturb my partner on the king size?
Open coil cores move as one unit, so you'll feel more of a partner's movement than you would on pocket springs. The king's 75cm each of width helps, since you're further from the disturbance, but if one of you gets up hours before the other, expect to notice it.
Should I choose this mattress in a UK king or a UK double?
If your room meets the 2.7m x 2.9m we suggest for a UK king, take the king: it's 15cm wider and 10cm longer than the UK double, and on a firm surface that extra width means neither of you sleeps pinned to your edge. In a smaller room, the UK double is the sensible pick.