Suitable topper on a medium/soft mattress

Hi
I bought a medium/soft Kingsize divan bed and mattress (Artisan, I believe) a couple of years ago. I also bought a wool fleece topper from DPW.
I have replaced the divan with a slatted 4 poster and discarded with the wool topper. The bed is now less comfortable.
What topper should I buy, bearing in mind our weight differences, as reflected in variable mattress firmness, of me (14st) and my wife (8st)?