We ditched the memory foam once it sag and compacted. Never again! I went shopping, bought the high coil count firmest mattress with box spring (Sealy Posturpedic...my favorite brand for years) . AND...then I bought a 1.5" thick memory foam mattress for on top of our very firm mattress. Love it!! Been almost 2years and still comfy.
Mattress sets are difficult to compare due to the marketing of each per each retailer. (Lots f model numbers per same mattress). Just go lay down on a lot of them until one feels right.
Good luck.
Sandy