Hi fascinating-geology,
I don’t know that I have too much more that I can add from my replies to your posts back in December when you asked about the same thing, but I’ll try to clarify a bit.
Being of a higher BMI, it is imperative that you have stronger deep support, and also more sufficient, slightly firmer and higher quality comfort layers. This has been shown through your own experimentation with poor results with mattresses being “too soft” per your explanation, and ones using lower density foams (Simmons, Stearns & Foster, air mattress).
A high BMI presents special challenges and generally requires firmer materials (in the support layers especially). This could be firmer latex or innersprings (the type of support component would be a personal preference and in the right design either could be suitable) or even a zoned construction. The same overall guidelines apply with higher weights though that PPP (Posture and alignment, Pressure relief, and Personal preferences) along with using high quality durable materials that will maintain their feel and performance for longer periods of time are the way to make the best choices. Heavier people in general will need firmer and thicker comfort layers and firmer support layers than those who are lighter and because no materials will last as long with much higher weights the quality and durability of the materials and components is even more important than normal. I wouldn’t “rule out” any types of mattress and base your choices on your own personal testing. Post #3 here has more information and suggestions about heavier weights that is worth reading.
You had mentioned previously about wanting an innerspring unit to contour more and sticking with a pocketed spring unit, but in your case what you’ve been describing generally points to something that doesn’t have enough deep support and is also too plush in the surface comfort. Pocketed springs do allow for more conformation, but in your case (as I outlined in one of my previous replies), you may be better suited for an even stronger innerspring unit, as some pocketed spring units can contour too much for those of a higher BMI. Maybe something along the lines of a knotted offset, perhaps.
As for the padding layers, something more substantial than the lower density foams in some of the models you’ve chosen would make sense. Using a polyfoam of a higher density doesn’t necessarily mean that the foam will feel harder, but it will be more substantial and better able to help support and contribute to a more durable comfort for you. Take a look again at the information in post #3 (and what it links to) that I mentioned previously.
Regarding zoning, there are many variations out there. The most common is an innerspring where the middle third is a bit firmer to help provide a bit of extra support where people tend to be the heaviest. A five-zone system is more complex, and this is the one you mention. It is designed to let the hips sink in just a bit more (they tend to be a wider, heavier area of the body), but not to the point of sinking as if you’re in a hammock. The next zone under the lumbar layer would be a bit firmer to prevent that area from falling in too much avoiding the “twisting” they you are describing. FloBeds, a site member here, has quite a bit of expertise with true zoned mattresses and explains about this quite well in a video that you may find interesting on this page. There is more about zoning in post #11 here. Also in post #2 here and post #7 here (latex momzone unique properties).
Realize that while many mattresses may be advertised as “zoned”, very few carry this through all of the layers of a mattress and overall I would tend to focus first and foremost upon the appropriate componentry for your situation.
Besides the information I’ve listed above, I would also suggest you go back and re-read the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice, regardless of BMI, and perhaps more importantly know how and why to avoid the worst ones (like a few of the items with which you’ve unfortunately had bad experiences). Quite often you can find local manufacturers who are experienced with creating products using higher-quality componentry for those of a higher BMI. If you list your zip code, I can see if I am aware of such businesses near your area.
Phoenix