DN,
I know you’ve been very methodical with your testing, and I think your plan for tonight makes sense. Unzipping the cover and then trying different layer configurations should give you a better idea of whether the firmness or compression is the issue.
Since you’ve already explored so many mattress-related possibilities, it may also be worth considering whether something outside the mattress is contributing to the interrupted sleep. Sometimes it’s not discomfort that wakes us, but changes in our sleep environment. I have written about this extensively and there is real value in investigating it.
For example, using a computer or phone right up until bedtime can affect some people’s sleep because blue light may delay or disrupt the body’s natural sleep rhythm. Temperature is another factor. As we fall asleep, our core body temperature naturally drops, and it gradually rises again as we approach waking. If you become too warm during the night, that can sometimes lead to more frequent awakenings or restless sleep, even if you’re not experiencing pain or pressure points.
I’m not saying that’s necessarily what’s happening here, but given everything you’ve already tried with the mattress, it may be another variable worth considering. There are products like the Perfectly Snug Smart Topper that actively regulate sleeping temperature throughout the night, though something as simple as adjusting room temperature or bedding can also make a difference.
Hopefully tonight’s test with the cover gives you some useful information. I’m interested to hear what you find. But do give other environmental factors a thought. Even use brown noise or some other sound and scent device. My wife can not seem to fall asleep without that sound machine on her night table.
At this point, you might as well test every theory, even if a bit unconventional.
Maverick