Hi re_vogel,
A forum search will bring up much more information about each of them. They are all included in the list of the better online memory foam sources I’m aware of and Restava is also a member here.
They are completely transparent and will provide the density of all their foams to any of their customers when you talk with them.
They use 3.7 lb, 4.1 lb, and 5.2 lb memory foams depending on the model. The 3.7 lb memory foam is “close enough” to a 4 lb memory foam that I would treat it as being closely equivalent (see post #4 here).
You’re correct and this may be one of the factors that may be an important part of some people’s personal value equation.
All of these would be inside the density guidelines that I would use so I wouldn’t consider any of them to have any weak links (as long as the mattress you are looking at is weight appropriate).
You are certainly looking at some good options and I know it’s always tough to make a final choice when you are making comparisons between good and good.
Phoenix