What type of mattress is bed for me

Hi I need some advice on which one of your mattress you would recommend. I'm 5ft.8 and 14.5 stone and my wife is 5ft.6 and 11 stone .I suffer with lower back pain an shoulder pain and I'm a back and side sleeper .the mattress we have currently is a 5 year old posturepedic pillow top which is dipping and it's to firm I'm my opinion and lacking in support I don't know what firmness it is rated at .Any help advice would be great full, I need a decent nights kip for the first time in a few years and get rid of the aches I wake up with .thanks dom