What the mattress sits on makes a big difference.  A sprung divan base, or box spring, gives the mattress the best possible support, adding to the comfort and extending its life.

A slatted base has a degree of flexibility, but cannot match a sprung base, and can damage a pocket sprung mattress as the gaps create areas where the mattress is not supported.  A firm base gives level support, but will firm the mattress up and reduce its life.