Memory foam is a high-tech material invented by NASA in the early 1970s to protect astronauts from G forces during liftoff. This technology was adapted to the consumer market as an alternative to traditional spring and coil mattresses.
The first consumer memory foam mattress was introduced in Sweden in 1991. The term "memory foam" evolved to describe the foam's unique characteristic of conforming to a person's shape, then returning to normal when the person arises.
Regular mattresses retain their shape and firmness by using an array of steel springs and coils, topped with layers of foam, polyester or cotton batting.
A quality foam mattress should not need a spring mattress beneath it to feel comfortable. Cheap imitations might feel good at first but will collapse quickly.
A regular mattress with the appropriate spring load should be your choice if you prefer an exceptionally stiff or exceptionally soft sleeping surface. Memory foam is available in varying degrees of firmness, but the sleeping experience is completely different.
Whether to buy a memory foam or regular mattress comes down to personal preference. Before spending a lot of money, look for a 30- or 60-day in-home trial period, as well as a good warranty.