Hi Mauch66,
There have already been some good replies here but hopefully I can add a few more thoughts that will be helpful as well.
Just in case you haven’t seen it … post #12 here has a link to some of the better quality/value online memory foam retailers and manufacturers I’m aware of. Most of these use a widely available major brand mattress (often Tempurpedic but sometimes Sealy Optimum or Serta iComfort as well) as a reference point for comparisons so for most of their mattresses you would have a local mattress you could test which along with your conversations with them could give you a good sense of which of their mattresses may be the best match for you in terms of PPP.
There are several ways that one mattress can “match” another one. These are primarily the equivalent comfort/pressure relief and support/alignment, the quality/density of the materials, the design of the mattress in terms of the thickness and order of the layers and similar foam densities, and finally the part which is much more relative and subjective which is the “feel” of the mattress. There is more about all of this in post #9 here.
For most people … the relative softness/firmness or “equivalence” in comfort and support would be the most important part of matching one mattress to another because this would be the most obvious part of their normal sleeping experience. Of course the quality/durability of the materials and the design also are important in terms of how closely one mattress may match another and in their relative durability but this is easier to assess based on comparing the specs of the mattress.
Finally … the “feel” of a mattress can also be important but this is purely subjective and this is the part where each person may have a different opinion. I don’t have any personal experience with any of the mattresses on the list so I’m not really qualified to say which one I think would be the closest comparison in terms of “feel” and even if I had, other people may have very different opinions because this is so subjective and relative to the body type, sleeping style, and perceptions of each person.
When you are “matching” a local mattress to an online mattress then the return or exchange policies may also be an important part of your personal value equation just in case what you “feel” on a mattress you purchase doesn’t match your ideal or the perceptions or assessment of other people or the manufacturer.
All of the choices on the list are certainly good quality/value options but hopefully this will give you some reference points that you can use to compare them with the equivalent major brand mattress you have tested or with each other and decide which one of the many “good vs good” options you have available is the final choice that is the best option for you.
Phoenix