Memory foam ‘visco elastic’ is a close cell elastic construction that is slow recovering and will follow the contours of your shape reducing the cold air pockets, thus creating a less disturbed nights sleep.
Memory foam has very low resistance strength and has to be used either on a high density foam block or on springs to work correctly.
Memory foam on its own is a topper and lays on top of a mattress
A memory foam mattress will be warmer than a non memory foam mattress especially a memory foam/foam type construction, consider a sprung interior mattress or one with a heat reduction covering!