Hi BackPain100.
Avoiding the lower end mattresses that use lower quality and less durable materials is a great start …I applaud your decision. 
While I’ve seen that you already reached out to Luma Sleep one of our Expert members I’m not sure what you’ve read since you found our site …and just in case you haven’t read it yet … the first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and of course how and why to avoid the worst ones.
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 “comfort”, firmness, and PPP that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for 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 (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
Support/alignment and comfort/pressure relief are the two most important functions of a mattress for everyone so you’d need to determine with each mattress that you are considering whether it will be a suitable choice that provides you with both based either on your own careful testing and personal experience when you sleep on it (and some local testing may give you a great deal of information and help you narrow down your choices … or/and…as you are already doing … seeking the guidance from an /knowledgeable and experienced expert retailer/manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using (resilience, firmness etc.) 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 or other mattresses you are considering 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 and firmness levels to different body types, sleeping positions, and preferences or to other mattresses that they are familiar with than anyone else.
Good luck with your search. You are on good hands with Luma
Phoenix