Hi barneycalhoun,
Even with the number of threads you may have read through, I’d caution against using the experience of others, on this site or elsewhere, as a reliable indicator of what might be applicable for you or others, as nothing can replace one’s own careful personal testing of a product. Even two individuals with the exact same dimensions and mass can have dramatically different needs to achieve personalized comfort. Additionally, the top 2" or 3" layer of a mattress is just part of a total sleep system that works in unison with all of the other layers (although changes in the upper layers are the most noticeable in any component mattress system).
I would be remiss if I didn’t comment that overall, plushness is overprescribed in the mattress industry, and alignment issues can arise not only from poor support systems, but also from too thick or too soft comfort layers (as you alluded). The ideal is to have both suitable support/alignment and comfort/pressure relief in a mattress. But if you have to choose one over the other then I would choose support/alignment. There is some great information in this PHD thesis by Vincent+Verhaer (who is one of a group of researchers that I greatly respect) about the importance of good spinal alignment that clearly indicates that for healthy individuals it has the single biggest effect on the depth and quality of sleep and recovery for healthy individuals. Having proper alignment doesn’t necessarily mean that a mattress needs to feel hard like a board, and in any situation you certainly would want some surface comfort along with this deep support.
You are correct that latex over a Marshall/pocketed coil system is a very popular combination, for all populations. I don’t have the specifics of the pocketed spring unit in the Luma system you referenced, but by appearances I believe it to be one of the Quantum Edge units from Leggett and Platt. These are high-quality spring units and are rarely the weak link in a mattress. Many manufacturers choose to keep the information about their spring units (producers, gauge of steel, turns) proprietary, as unless you are extremely knowledgeable about innerspring and their designs (which would be very few individuals in the country) the information would only serve those who are attempting to copy their design. With that being said, Luma is very transparent about their materials and I’m sure they would provide you with as much information as they were comfortable doing.
If you’re interested, there are many factors that determine how a particular innerspring will feel and perform inside a specific mattress design. There is more about the different types of innersprings in this article and in post #10 here but I would pay much more attention to your own careful and objective testing which will tell you how the innerspring performs in combination with the other layers and materials in a mattress and to the quality of the materials above the innerspring which is normally the weakest link in a mattress. Post #16 also talks about different innerspring designs and how they work.
Phoenix