Hi djgoldb,
Zoning can certainly be a good solution if you have a body type that is more challenging to “fit” to unizoned layers but I would also keep in mind that “ruler straight” alignment isn’t necessary or even possible in most cases. As long as your design keeps you in the alignment range that doesn’t produce “symptoms” when you sleep on the mattress then it would be fine. There is more about zoning in post #11 here and the posts it links to that may be helpful but of course with any combination of layers or zoning patterns the only way to know whether it’s a good match for you in “real life” will be based on your own personal experience.
There is more about the most common symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here.
There is also 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” and “pressure relief” and “feel”.
These posts are the “tools” that can help with the analysis, trial and error, and detective work that may be necessary to help you learn your body’s language and “translate” what your body is trying to tell you so you can make the types of layering changes that have the best chance of reducing or eliminating any “symptoms” you are experiencing.
If you are experiencing upper back pain from shoulders that don’t sink in enough then some of the other options that may help are either a softer top comfort layer such as the 19 ILD layer you have which would be the next increment softer and would help your shoulders to sink in more deeply than softening the middle layer or your “symptoms” could also be the result of a pillow issue. Some of the information in posts #2 and #3 here may be helpful as well.
You can do either depending on the effect you are looking for. Zoning the top layer can have a bigger effect on the “feel” of the mattress and on how deeply your shoulders are able to sink in relative to your hips/pelvis and zoning the deeper layers can have a bigger effect on how deeply your hips/pelvis sink in relative to your shoulders without sacrificing pressure relief under your hips. The effects of zoning in the deeper layers will be more subtle than zoning in the top layers. In other words if the main issue is how deeply your shoulders are sinking in but the firmness under your hips/pelvis is fine you can use zoning to “allow” your shoulders to sink in more deeply by softening the shoulder zone in the top layer. If the main issue is that your shoulders are fine but your pelvis is sinking in too much then you can zone the deeper layers to “stop” the hips from sinking in too deeply by firming up the middle zone in the deeper layers without affecting the pressure relief under your hips.
While I haven’t personally tried a combination of memory foam/latex zoning … I would hesitate to use it because the materials are too different from each other and I would tend to use the same material in top surface zoning layers so that the sleeping surface is consistent in terms of feel and response other than firmness levels and using memory foam in deeper zoning levels can prevent the memory foam from responding the way it’s designed to and can firm up the memory foam compared to using it in the top layer.
I’m a little lost and unclear about the specific details of the all the exact combinations of layers you have actually slept on for a few days or longer and how they specifically compared to each other in terms of the “symptoms” you experienced in each of them but if I’m not mistaken you have a 19 ILD layer anyway so I would try using it instead of your current 24 ILD top layer to see how it works for you before going to a 14 ILD layer.
If you can write a post that recaps the specifics of each layer combination that you have tried for a few days or longer (listed from top to bottom) in bold and then make some comments about the specifics of how each combination differs from the others and the types and “direction” of the changes you noticed relative to the one before it underneath each layering description it would also be helpful and be a more useful reference to see them all together.
I don’t know off the top of my head which of the suppliers in the component list sell custom sizes so you may need to call them and ask. I would try KTT and SLAB (they sell odd sizes in their scrap section) to see if they have any odd sizes available that would either be the right size for the zone you want or that are only a little larger and wouldn’t need to “waste” most of a layer.
Phoenix