Hi Dan1979,
There are really only two ways to choose a mattress in terms of PPP (see mattress firmness/comfort levels in post #2 here). One is your own careful and objective testing and experience and the other is based on more detailed conversations with an online (or distant) retailer or manufacturer so they can help you choose one of the mattresses that they offer that has the best odds of being a suitable “match” for your specific needs and preferences based on “averages”.
Other than that you would be looking at trial and error and going through the learning curve that is involved in becoming an “expert” in mattress design and theory which would take many weeks, months, or years and a great deal of experience testing different types of mattresses and materials so you have some reference points and the specs you are looking at have some “meaning” to you in your own personal experience. There are just too many unknowns, variables, and personal preferences involved to use 'theory at a distance" as an effective way to choose a mattress.
Polyfoam and latex use different methods to test for ILD so they are not comparable (see post #6 here).
Two layers that are glued together will generally feel slightly firmer than the same two layers that aren’t glued … but many people may not notice the difference depending on the specifics of the layers and the rest of the design and components of the mattress.
Phoenix