Hi dorglet,
If your “sinkhole” is 1.5" or more then it would be covered under their warranty (see here). If on the other hand it is the result of foam softening and any visible impressions are less than the warranty exclusion of 1.5" then unfortunately it wouldn’t be covered by a warranty (see post #4 here).
You can read more about the Pranasleep mattresses in post #3 here and in post #2 here and in post #3 here. A forum search on Prana (you can just click this) will also bring up more information and feedback about them. I would be cautious because they use thicker layers of relatively low quality/density polyfoam in the quilting layers than I would be comfortable with (see the guidelines here) which could be a significant part of the reason for the issues you are having.
While latex is generally the most durable of all the foam materials … even with latex if the comfort layers are too soft for your body type then it can be a durability issue as well. There is more about all the variables that can affect the durability and useful life of a mattress relative to each person in post #4 here.
There is also more about the different types and blends of latex in post #6 here and as you can see 100% natural Talalay can also be less durable than other types or blends of latex in lower ILD’s.
If you take all of these factors together then it could certainly account for any visible impressions or “virtual impressions” in your mattress.
I’m not sure which of the Dreamfoam mattresses you are considering but if you are considering one of their latex hybrids then there is more about a latex/polyfoam hybrid and an all latex mattress in post #2 here. There is also more about the most important parts of the value of a mattress purchase in post #13 here.
The choice of materials is always a personal preference so there isn’t a “best” material for any particular person but I would make sure that no matter which type of materials or components that you tend to prefer and are in your mattress that you make sure that there are no weak links in the materials or design because all materials and components have higher quality and more durable and lower quality and less durable versions.
The better options or possibilities I’m aware of in the South Florida area (Miami/Ft Lauderdale areas) that may be worth considering are listed in post #2 here.
Phoenix