A lot of big name mattress sellers speak in their gimmicky marketing terms to obfuscate the true nature of their product.
Foam Mattress Pads Memory Foam Platform Beds & More
Check it out. (You can trace the pattern of your RV mattress on a big piece of paper, fold it, and mail it to them. They will custom cut for a reasonable price.) I think this place equates price with quality.
There are 3 types of foams: conventional foam (petrol), visco memory foam (petrol), or natural latex (rubber tree sap, very durable but heavy).
All of them (whether cheap or pricey) can come in any level of INITIAL firmness and comfort. Usually, more expensive the mattress is more heavier and denser the foam is per cubic foot, which provides durability in long term.
The density, or weight of the mattress does not correspond to the softness or firmness. You can certainly have a foam that is light but firm -- the problem is a mattress like that won't last many duty cycles.
What's great is that you can create a mattress by specifying the firmness of each of the 3 layers.
When I learned that Tempur-Pedic is merely a visco memory foam top layer glued on conventional foam core albeit designed carefully, I felt being cheated.
Perhaps for many of you, the price for a quality mattress may not justify the utilization. In theory, cheap foam can save weight and can provide the similar comfort of expensive foam for the occasional RV camping.
Another option:
Memory Foam Mattresses | Memory Foam Mattress Foundations | Memory Foam Pillows