Hi dorglet,
Knowing the quality and durability of all the layers in a mattress and avoiding a mattress that has a weak link in the materials (such as the quilting layers in your mattress that are over the latex) would be even more important than the firmness of the mattress. You can test a mattress to make sure that it’s suitable for you in terms of PPP (using the testing guidelines in the tutorial post) but you can’t “feel” the quality of the materials because lower quality and less durable materials can “feel” the same as higher quality materials in a showroom … they just don’t last as long before they lose their comfort and/or support (and comfort/support aren’t covered by a warranty).
There are many types of mattress that are lighter than the “mostly latex” mattress you purchased (such as a mattress that uses latex in the upper layers but polyfoam in the support layers) that would be easier to either rotate and flip (if they are two sided which is less common) or just rotate (if they are one sided) but it’s always a good idea to rotate or flip your mattress on a regular basis … especially at the beginning (see post #2 here). Again though … the most important part of avoiding softening or impressions is to make sure there are no weak links in the mattress … especially in the upper layers of the mattress which are generally the first to soften and break down.
The better local options and possibilities I’m aware of in the Port Charlotte, Fort Myers, Cape Coral, Naples, FL area (always subject to the guidelines here) are listed in post #2 here.
Phoenix