Hi Rink,
[quote]I guess I got the wrong impression. I had read this:
https://mattressunderground.com/mattress-...oe-alexis.html#20482[/quote]
From the first post this was a general comment about how two layers of latex could beneficial in certain situations with the Dreamfoam Aloe Alexis mattress (and certainly others that are similar)… because it has both a latex comfort and transition layer and would be the “next best” thing to an all latex mattress. This would be especially true for someone who was either heavy enough to “go through” the top layer more because of their weight (the extra 3" transition layer being beneficial over the single 3" upper latex layer) or someone who was a side sleeper (regardless of weight) which is a more “curvy” sleeping profile than back or stomach sleeping ( where a person often won’t need as much latex in the comfort layers) where the better contouring properties of the middle latex transition layer can “help” the comfort layer and make a difference in how well the mattress adapts to their body shape and different sleeping positions. And also I summarized at the end…the only significant reason to choose one layer of latex over two IMO would be either budget, because someone was lighter and/or a back or stomach sleeper that didn’t compress much more than the top layer and wouldn’t “feel” the deeper layers as much, or if for some other reason the added benefits of the middle latex layer was less noticeable for a specific person.
So there isn’t a specific recommendation of 3" over 6" of comfort layers of latex (or any combination in between) in this situation, but instead general guidelines for someone who would have higher mass (or a side sleeper with a “curvier” body) and what they might like over a HD polyfoam core, versus someone who isn’t as of high of a mass, or someone who sleeps on their stomach or back. And these differences might change depending upon the “support core” piece changing from HD polyfoam to a pocketed spring unit that offers more conformation. But they certainly can be used as good general guidelines. Making specific recommendations isn’t something that is possible or that I do, because there are simply too many variables involved and only you can feel what you feel. But you can certainly use these guidelines as a good starting point!
[quote]and this:
https://mattressunderground.com/mattress-...ones-exist.html#9345[/quote]
The second link you mentioned is a bit more detailed analysis for a member in a bit of a different situation at about 200 pounds, and it restates what the first post discussed but in more detail and more specifics about all-latex products. I summarized…So the overall thickness of a mattress that is either “needed” or “preferred” would depend on the combinations of the layers and components that are needed to achieve the design goal of the mattress and provide the PPP (Pressure relief, Posture and alignment, and Personal preferences) that can best match each person and their unique body type, sleeping positions, and preferences.
In general, the extra layers you are asking about can be useful for someone in a higher BMI, or someone with a somatotype with a larger difference between the shoulders, waist and hips, or someone who sleeps mostly on their side or side/back. People who sleep on their stomach, stomach/back, are less “curvy” or of a lower BMI may desire/prefer/need less amounts of comfort layer materials. Comfort/pressure relief and support/alignment are the two most important functions of a mattress for everyone so the only way to know for certain whether any specific mattress will be a suitable choice that provides you with both will be based on your own careful testing or your own personal experience when you sleep on it because different people can have very different needs and preferences in a mattress in terms of comfort, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences). If you want to learn a little more, 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” and “pressure relief” and “feel”.
I hope that helps clarify my comments from the earlier posts you mentioned and puts them in a better perspective. 
Phoenix