I have a bed from Dreams that is causing more problems.

I have hyper lordosis, scoliosis, spondylosis and bulging of cervical and lumbar discs and I'm 17 stone in weight. I need a firm, supporting bed. My partner is 10 stone and also has scoliosis. We prefer king size. Is there any bed that can offer extreme support and comfort without bowing or sagging as my current pocket sprung orthopedic bed from dreams has been ridiculous from a few months post buying, 3yrs ago.
Before that, I had a similar type of bed, very firm and no turn. That one lasted 15yrs! So I'm hoping you can help.