Hi Ya,
Post #6 here has more information about the different types and blends of latex. There is also more information in post #7 here about the difference in “feel” between Talalay and Dunlop but the best way to know which one you prefer would be based on your own personal experience.
This is one of those “what is the meaning of life?” types of questions where it could take a book (or many) to answer in any depth. In very general terms the layers closest to the top of a mattress are more about comfort/pressure relief, the layers closer to the bottom of the mattress are more about support/alignment and layers in the middle or “transition layers” can help with both. There is more information in the mattresses section in the main menu of the site that goes into much more detail about different types of mattress designs and construction there is some general information in post #4 here that may also be helpful.
If you can’t test a mattress in person for PPP though … then I would make your choice based on a more detailed conversation on the phone with SleepEz (see mattress firmness/comfort levels in post #2 here) because it’s much easier to work with a knowledgeable and experienced manufacturer who already knows what you would otherwise need to learn than to try and become an expert yourself.
Phoenix