Hi cnc factory,
That’s a pretty broad question because there are several different types of foam which have very different properties and feels. They include memory foam, polyurethane foam, and latex foam.
While I understand the need for softness on top which can provide better pressure relief … it’s also important to know that softness on top doesn’t mean that you can’t also have firmer underneath so that you can also have good alignment as well. If the entire mattress is too soft (instead of just the top layers) there is a risk that you would have the pressure relief you need but not the posture and alignment which can be even more important. Mattresses are always both soft and firm in different areas and the trick is to find the best combination of the two. The mattresses section of the site has several overviews which can give you some basic information about mattresses and materials that may help point to what your best choices may be.
Some of the better outlets in the San Diego area are in post #2 here. The thread is about latex mattresses (which are likely outside of your budget range), but most of the manufacturers and outlets there carry other options as well including good options inside your budget. I would call them first to confirm what they have available that fits your budget and preferences before I made a visit. The first two on the list would be where I started.
Phoenix