What mattress to choose

We are looking to buy a mattress we currently have a king size latex topped sprung mattress on a divan bed which is now over 10 years old and lost it's comfort. We both suffer with bad backs sleep on our sides on the edge of the mattress and weigh between 12 and 14 stone being 5ft 2 inches and 5ft 7inches.
While we would look to replace the bed with something similar we would be open to suggestions for example your full latex range would they offer enough edge support.
We would be obliged if you would offer your advice.