Hi mncurtis,
The materials in the Serenity are all high quality so there are no weak links in the mattress.
It’s unusual for a memory foam mattress to be sold with a box spring because they usually use a firm non flexing foundation but if your testing indicates that the mattress / boxspring combination is a good match for you in terms of PPP then I wouldn’t have any concerns about it’s durability. You could also ask to test it on one of their adjustable beds (if they are willing to do this) to see if it works better for you on a box spring or a firm base.
There are many factors that in combination with each other can affect sleeping temperature (see post #2 here) but memory foam tends to sleep warmer than other types of foam so if your experience indicates that sleeping hot is an issue then at the least you may want to make sure that you have covered all the other factors that can affect sleeping temperature and if your experience or history indicates that it’s a more significant issue for you then you may wish to avoid memory foam comfort layers. It may also be worthwhile taking a nap on the floor model for about 30 minutes of so to see if there is any indication that you would tend to sleep warm on it.
Phoenix