Mattress advice for back problems

Hello, I really hope you’ll be able to offer some advice which will finally be able to solve our ongoing dilemma about which type of bed / mattress to buy. I am 5 ft 4 in and weigh 8 st 7 lb and my partner is 6ft 1 and weighs 14st. We both have a history of back problems, mine is currently exasperated by the firm mattress we sleep on and the size of our bed which is a standard double and too small. Whereas my partner likes our firm mattress, he bought it some time ago to remedy his back problems and has found it works well. When we’ve been on holiday and he’s slept on mattress’s that have been softer his back pain always returns. To add to the problem I struggle to fall asleep and my partner complains that I constantly toss and turn. So as you can see bed time’s not very relaxing in our house !!!

Our budget is around £800 and whilst I’d love a super king our room is only big enough for a king size. I’m also confused as to which type of base to buy as this can significantly increase the cost – particularly as we like something with as much storage as possible or perhaps a regular bed frame would suffice?

I’d be very grateful for any advice you can offer . Many thanks, Tanya >