Choosing a mattress

I am 8.5 stone and have lower back and neck and shoulder problems. I liked my previous memory foam mattress, but after 7 years it has become saggy and uncomfortable. I wonder if you can recommend a mattress for me. I would prefer to go for foam or latex as I have had bad experiences with sprung and pocket mattresses in the past, although I am open to any suggestions. My husband is around 11 stone with no significant back issues.