Hi jctiltz,
This is certainly correct and slight variations aren’t uncommon.
Unfortunately it’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress. There are just too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
Firmness suggestions from a manufacturer are generally based on the “averages” of other people that are in a similar weight range and have a similar sleeping style to yours but there are also some people that are outside the averages of other people and in these cases the only way to know for certain whether any layering combination will work well for you will be based on your own actual experience.
I don’t know the ILD of the polyfoam base layer but ILD for polyfoam and for latex aren’t directly comparable anyway (they are measured in different ways so the ILD numbers don’t correspond to each other). ILD is also only one of several factors or “specs” that will determine how soft or firm an individual layer will feel to different people and can often be more misleading than helpful when it comes to assessing a mattress “as a whole” (see post #4 here).
Having said that … based on your comments and your experience on the single layer (although it was only for a very short time) your thought process certainly makes sense to me. I’m not sure how long you have slept on the 24 ILD over the 32 ILD but I would make sure that it’s been for more than just a few days so you can identify any consistent patterns in your experience rather than just assessing your experience over the course of just a day or two which could be an anomaly or the result of adjusting to the change itself. I’m also not sure how this combination affected your shoulders.
The firmest layering combination that would currently be possible with the layers you have would be the 32 ILD layer over the 24 ILD layer so it may be worth trying that combination for a few days to see how it affects your back as well.
If you have tried all the different combinations that are currently possible and decide to do an exchange I would probably try exchanging for a 36 ILD layer and this will give you 4 layers to work with so you could experiment with different layering combinations (such as the 19 ILD over the 36 ILD or the 24 ILD over the 36 ILD) and then you could decide on which layer to return and which to keep based on your actual experience on different combinations.
I would also prioritize alignment and lower back pain over pressure relief (although of course having both is ideal) because outside of certain medical conditions alignment is the single most important factor in how well you sleep at night and your body’s ability to rest and recover over the course of the night.
Phoenix