Hi diversification,
The amount or total thickness of polyfoam in a mattress isn’t a meaningful issue (unless for some reason someone wants to avoid polyfoam completely) … the more important issue is the quality/density of the polyfoam and how much of any lower quality/density polyfoam is in the upper layers of the mattress. The single biggest factor in the durability and useful life of a polyfoam material is the density of the polyfoam but the firmness of the polyfoam and the position of the polyfoam in the mattress (close to the top layers vs deeper in the mattress) will also play a role in durability as well. There is more detailed information about the many variables that can affect the durability and useful life of a mattress in post #4 here and the other posts it links to.
There is more about the different ways that one mattress can “match” or approximate another one in post #9 here. While you may be able to “match” two mattresses in terms of their expected durability by looking at the quality and durability of the materials in a mattress … you can’t “match” the feel and performance or the suitability of two mattresses in terms of PPP by comparing foam or design specs unless you have two mattresses where the type, thickness, and firmness of all the layers are virtually identical which would be very unlikely.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for (or that doesn’t feel as close to another mattress as you hoped it would) that are involved in each of them and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability, durability, and value.
When you are considering an online mattress that you can’t test or compare to another mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs to different body types, sleeping positions, and preferences or to other mattresses that they are familiar with than anyone else. If you are purchasing an online mattress then the options you have after a purchase to return or exchange the mattress if it doesn’t turn out as well as you hoped for (or doesn’t match another mattress you were using as your target as closely as you hoped for) would also become a much more important part of the “value” of your purchase.
Phoenix