Hi groggy23,
The best suggestion I could make would be to make sure you do some careful testing for PPP using the testing guidelines and make sure you test any mattress you are considering together. I would also make sure that you know as much of the specifics of all the layers and components in the mattress you are exchanging for as possible to make sure there are no weak links in the mattress or you could end up with a mattress that you test for PPP and works well for a while but then the softening or breakdown of lower quality materials (in the comfort layers especially) can lead to the loss of comfort or support and the return of your symptoms.
Generally your symptoms would be the result of an alignment issue which can often lead to the muscles working over the course of the night to keep you in alignment (instead of the mattress) which can lead to back pain and/or stiffness in the morning.
The Latechs cushion form doesn’t list any of the specifics of the layers except that there is 2" of some kind of natural latex (probably blended Talalay) in the comfort layers. The so called “engineered latex” is polyfoam and I would want to know the density of the polyfoam layers in the mattress which could be the weak link of the mattress. It is probably similar to the Boyd 950 mattress here (the Latechs is made by Boyd) except for the cover. You can see some prices for reference for the Boyd 950 here.
the Tempur Rhapsody Breeze uses high quality memory foams (7 lb and 5.3 lb) but of course is not good value compared to other mattresses that use similar quality materials.
I would be very cautious with Stearns & Foster because they don’t disclose the density/quality of the polyfoam in their comfort layers and they are generally lower density and would be the weak link of the mattress.
Post #2 here also has more information and some links to other threads on the forum that are about exchanging a mattress at a store where your options are more limited that may also be helpful.
Phoenix