Hi there WitsEnd,
I’m really sorry to hear you can’t seem to get everything working together. I know how frustrating that kind of long-term, no-clear-answer situation can be.
I went back and reviewed your original post along with your recent updates. What stands out to me is that you’ve been fairly methodical in working through different latex configurations, yet the underlying issue still seems to remain the same.
At 5’10" and 135 lbs, you’re not someone I would typically expect to be overpowering medium or firm latex layers. That’s why your continued reports of pelvic sinkage and alignment problems are so interesting. The fact that your upper body barely seems to sink while your hips feel like the anchor point suggests there may be more going on than simply choosing the wrong latex firmness.
I also found it interesting that the shikibuton on a hard surface came closest to providing relief, even if only temporarily. The fact that it doesn’t really “give” much but still felt the most comfortable for a short time is somewhat telling, and I can see how that pattern would develop based on what you’re describing. It points to you being quite sensitive to even small amounts of hammocking or differential sinking through the mattress. I can also know that the failure of the shiki to rebound back might be an issue. I had a similar thing happen with my 3" organic wool topper, but for me the wool not rebounding only looked bad, due to the body impressions left. At the same time, the body impressions resulting from the wool topper, allowed the topper to conform to my body and ultimately I was actually quite comfortable.
Given everything you’ve tried so far, I’m thinking it might be worth exploring a different support system altogether rather than continuing to swap latex layers. A pocketed coil support unit, such as the Quad Coil from Pocket Coil Store or something sleepez could offer, combined with latex comfort layers, would provide a very different support profile than an all-latex build. A pocketed coil system may work better because it can provide more targeted support under the pelvis while still allowing the rest of the body to settle more naturally. Whether it would solve the problem is impossible to say, but it may be worth considering since you’ve already gathered a lot of information about what does and doesn’t work for you in an all-latex configuration.
In situations like yours, sometimes the biggest breakthrough doesn’t come from changing firmness levels, but from changing the support design itself.
Just my thoughts based on what you’ve shared so far.
One more thing I would assume, you probably already have this dialed in, but just in case, it’s worth making sure your foundation is solid with narrow slat spacing (under 3"), rigid slats that aren’t flexing, and slats that are at least 2–3" wide. Your foundation can make a bigger difference than people expect, and it’s easy to overlook when you’re focused on the mattress layers themselves. Also, since you’re a back sleeper, pillow loft and fill can be more important than it seems at first. Something like the Oxygen Pillow or Helix Adjustable Pillow could be worth a look just for fine-tuning head and neck alignment. Remember, everything between you and the floor matters, including your duvet, sheets, how tightly that hug the mattress, and how your mattress protector sits and fits on the mattress.
Hopefully this gives you some food for thought.
Maverick