A few points to ponder.
1 Memory foam, go to a store with mattresses, try a memory foam mattress, lay on it for awhile. Memory foam mattresses feel a bit different imho i prefer them but its what you like that matters for you. Obusforme makes a good one, so does Tempurpedic and iComfort. Cheap ones aren't very nice. Generally cheap ones are very firm and have lousy consistency (some firmer then others). Also if you get one rolled up (Mattress/topper) give it a few hours to expand before you try it.
A memory foam mattress/topper can be infused with cooling beads (by nature they're warm) there are some that have a solid "blue" and others that are like dots. Generally the solid ones hold temperature more consistently. With my memory foam pillows one side has cooling foam the other doesn't (flip for winter/summer).
Any topper can only be as good as the mattress below it. If the mattress is just lacking padding but still has good support (the wires/coils aren't dislodged, compressed, broken) then a topper can make a bed softer and fill in those "voids" with the natural curvature of the spine and body (lets face it very few of us are shaped like a 2x4). If its a newer OEM mattress and you are somewhere south of 700lbs a topper may offer improvement. If your mattress is worn, well a topper is like putting a fresh coat of paint over rotted luan. Not really going to do much good.
The "best" solution would be a new mattress (short or normal depending on your unit), closest to your ideal s&b mattress. Keep in mind though the "best" mattresses are heavier and can eat into your ccc's and/or not be very good if your bedroom slide requires your mattress to contort to fit.
Generally more robust people will want a high density foam (exact same principal with car seats, robust people will want a wider seat with less bolstering and firmer support).
So short story if your mattress isn't worn a topper can add comfort, if not you'll need a better/newer mattress first. Has the mattress always been not very plush or has it gotten much worst recently? former topper should help, latter, Costco/Sleep Country/Store of Choice and try mattresses in person before you buy online. (Type/firmness etc)
A good mattress = better rest = more time to camp =