Hi DHC,
I or some of the more knowledgeable members of the site can certainly help you to narrow down your options, help you focus on better quality/value choices that are available to you either locally or online, help you identify any lower quality materials or weak links in a mattress you may be considering, act as a fact check, answer many of the specific questions you may have along the way that don’t involve what you will “feel” on a mattress, and help with “how” to choose but only you can decide which specific mattress, manufacturer, or combination of materials is “best for you” regardless of the name of the manufacturer on the label or whether anyone else has the same criteria or circumstances or would make the same choice.
Again you are the only one that can feel what you feel on a mattress and with careful testing … your own body will provide the best guidance about which mattress is the best “match” for you in terms of PPP. Unfortunately nobody has a crystal ball that can predict which specific mattress you will sleep best on with any certainty based on specs or “theory at a distance” … it just doesn’t exist.
Careful and objective testing using the testing guidelines in the tutorial post will usually result in a mattress choice that is well inside the comfort/support range that is suitable for you (see post #10 here and post #4 here) but if you are testing two mattresses that both appear to be very suitable choices in terms of PPP … I would generally prioritize alignment over pressure relief and “comfort”.
“Support” is often misunderstood and many people believe incorrectly that “firmer is better” or “more supportive” when the real goal is to keep the spine in good alignment and this requires the type of contouring support that allows some parts of the body to sink in more and some parts of the body to sink in less and this will vary on an individual basis. There is more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support/alignment” and “comfort/pressure relief” and “feel” and how they interact together.
The Dormio mattresses also have exchangeable layers so if in spite of “best efforts” on your and their parts you end up choosing a layering combination that isn’t quite right for you either in terms of comfort/pressure relief or support/alignment then you can also fine tune the mattress after a purchase by rearranging or exchanging layers so the risk of making an unsuitable choice is much lower.
While taking a picture of your alignment on each mattress and showing it to your Chiropractor would certainly be a good idea … especially if you are prone to lower back issues (which can often be aggravated by a mattress that is too soft) … I would also keep in mind that the ultimate test is whether you sleep well and “symptom free” on a mattress.
There isn’t a “formula” that can be used to assess or “calculate” value because there are so many different variables and criteria involved that are more or less important to different people that may be very different from someone else and because the “value” of a mattress purchase is always relative to how they compare to the other finalists you are considering or to the other mattresses that are available to you in the area or online based on all the parts of your personal value equation that are most important to you.
The quality/value guidelines I linked in my earlier replies can help you make more meaningful comparisons between the relative “value” of each mattress you are considering. While it’s not really possible to be specific about value relative to mattress materials and construction because there are so many combinations and variables involved (and a mattress that would be good value for one person may not have good value at all for someone else that has different needs and preferences, lives in a different area, or that is considering different mattresses) … this article may give you some sense of the potential benefits of different budget ranges.
As far as what you “should” be spending there’s really no definitive answer to this but I would suggest as much as you can comfortably afford … within reason and within limits of course. You will find better quality and higher performance materials and components and more sophisticated and complex designs in higher budget ranges but once you reach about $3000 or so (in US dollars and in queen size mattress only or the equivalent in a king size which are generally about 15% to 25% more) then any realistic or meaningful performance benefits that go with higher prices than this may be minimal and there would need to be a compelling reason and obvious benefits for me to spend more than that (again in queen size). Even then I would make some very careful value comparisons with other mattresses that are available to you based on the parts of your personal value equation that are most important to you because it’s quite likely that you will be able to find a high quality mattress in a lower budget range than this that will work very well for you. While it’s not really possible to be too specific about value relative to mattress materials and construction because there are so many combinations and variables involved … this article may give you some sense of the budget ranges that may be worth considering.
Once you are down to a list of finalists and you are confident that they would all be a good match for you in terms of PPP (or you have good options after a purchase if you aren’t) and that there are no lower quality materials or weak links in any of them in terms of durability (which there aren’t) then you would be down to finalists that are comparing “good to good”. If there are no clear winners between them at this point (which is usually a good indication that you have done some very good research) then you are in the fortunate position that any of them would likely make a good quality/value choice and (post #2 here) can help you make a final choice based on your local testing or mattresses you have slept well on, your more detailed conversations with each of them, your confidence about PPP and the suitability of each one, their prices, your preferences, the options you have after a purchase to fine tune the mattress or exchange or return the mattress or individual layers, any additional “value” extras that are part of each purchase, and on “informed best judgement” based on all the other objective, subjective, and intangible parts of your personal value equation that are most important to you. Sometimes a final choice may even come down to very minor differences or can sometimes just be a matter of “gut feel” or “educated best judgement”.
One of the benefits of dealing with the manufacturers or retailers that have been invited to become members of this site is that they all provide a bonus or discount on their mattresses to the forum members that purchase a mattress from them (see here). Of course they can only do this if you let them know you are a forum member here. While 5% certainly isn’t “make or break” in terms of value … everything helps 
Phoenix