Hi zab,
If you’re not interested in mattresses using latex, you missed Addable and Purple. Of course, that list is not complete for all simplified choice online mattresses available. Post #12 here has some of the better online memory foam options for those who are looking for a memory foam mattress, and many have cores 2 lb or above.
Yes, memory foam is not resilient and is more difficult to reposition on. You’ve mentioned before that you don’ like this feeling, which is why I’m curious that you aren’t looking at something using latex.
This mattress doesn’t use latex, nor does it use foam similar to the TitanFlex (which I described as more “buoyant”) so I wouldn’t expect it to have such a feel of being “buoyant”. I’m not sure why you would have an aversion to an innerspring unit, as that particular model did use quite a bit of polyfoam between yourself and the springs (so you shouldn’t feel the pressure points of the springs as you described previously), but if you decide to go that route then don’t test any models with springs on the inside to narrow down your focus.
There are many factors involved in form durability, which I cover in more detail here. I would have no concern between a total of 3" or 4" of a 4 lb polyfoam in general.
Phoenix