Hi adriatic,
All foam materials and mattresses will go through some initial break in period as the foam loses any of its “false firmness”, the cover stretches, and any fibers settle somewhat and compress. In general terms though … latex is the most durable of all foam materials and this softening and breakdown will be less and take a longer period of time than other types of foam (even if they are good quality). There is more about the many factors that can affect durability and the useful life of a mattress relative to different people in post #4 here and the posts it links to.
As a general foam category … latex is the “gold standard” for durability out of the different types of foam (polyfoam, memory foam, and latex foam).
If you know the materials are good quality and that any foam softening or breakdown will be minimal … then it’s usually best to choose a mattress that is as close as possible to your ideal in terms of PPP and not choose a firmer (or softer) mattress than you really need with the intent of compensating for softening over time. If you are “stuck” between two firmness ratings however then it’s usually better to choose slightly firmer than slightly softer because you can always add a topper to improve the pressure relief or comfort of a mattress but there is no great way to make a mattress that is already too soft any firmer without removing and replacing foam layers (see post #4 here).
Phoenix
PS: I see you found one of the links I mentioned in this reply while I was writing it 