Hi tismon,
the mostly latex comment was in reference to the Denver mattress latex mattresses which have been replaced by another model. What it means is that most of the layers are latex but that there is also some polyfoam in the mattress but that the polyfoam is in a layer where it won’t become the weak link of the mattress (either around an inch or so or less in the comfort layers or quilting or thicker layers in the bottom of the mattress under the latex).
As it relates to STLBeds … you could tell if any of their mattresses were “mostly latex” by making sure you have the details of all the layers in any mattress you are considering and then making sure that there was no more than around an inch or so of polyfoam in the comfort or quilting layers or that any thicker layers of polyfoam were in the deeper support layers of the mattress underneath the latex layers. “Latex hybrid” mattresses (a few inches of latex over polyfoam support core) often use a latex comfort layer over polyfoam support layers as a way to reduce the cost of sleeping on latex (you can see some comments about a latex hybrid vs an all latex mattress in post #2 here). I don’t keep a specific list of the design of mattresses carried by retailers (which are always changing and would be impossible to keep up with) so it’s always important to only consider or test mattresses where you are able to easily find out the type and quality of all the layers in the mattress so you can make sure there are no weak links in the mattress and can make more meaningful quality and value comparisons with other similar mattresses.
Phoenix