Hi Ty,
Foam by Mail doesn’t sell Talalay (in spite of what they say). You can read more about them in post #2 here and post #2 here. They are certainly not a source of latex I would trust. Your experience with evasive answers is their norm.
Some of the better sources of latex I’m aware of (including 100% natural Talalay) are listed in post #4 here.
Post #2 here has some links to some of the “theory” that may be helpful although they are generic and not specific to any person.
In most cases it’s easiest to just use a “standard” configuration that a manufacturer has had success with for people with your body type or sleeping style (such as 3 inch layers of S/M/F or M/F/XF or a 6+2 or 6+3 construction with appropriate support and comfort layers as examples) so that you don’t have to go through a long learning curve about mattress theory and design or how all the different specs interact together. It’s also a good idea if you are buying separate layers that you have good recourse if you make a mistake and need to return or exchange a layer.
Phoenix