Hi baddog,
There is no “correct” based on any formula or theory and the only “correct” would be the combination of layers that is the best “match” for you in terms of PPP and a combination of layers that you sleep well on.
There is more about the different ways to choose a mattress (either locally or online) that is the most suitable “match” for your specific needs and preferences and how to identify and minimize the risks of making a choice that doesn’t turn out as well as you hoped for that are involved in each of them in post #2 here.
Phoenix