Hi absolude,
This is one of the main factors in the the “conflict” between pressure relief and alignment and I’m glad to see you are taking this into consideration. Your support core is also softer than the norm so I would pay careful attention to your topper choice because of this. In general … “just enough” in terms of thickness and softness to provide good pressure relief is the “safest” choice in terms of alignment.
[quote]Also, not related to sleeping on the bed, I’d like to raise it a little and make it thicker so I don’t bottom out when sit on it.
Was thinking 2 or 3 inches of 19 or 21 ILD.
Any suggestions? [/quote]
The topper guidelines in post #8 here may be helpful in choosing a topper that provides the best “balance” between pressure relief and alignment. The height of the mattress wouldn’t play a role in my topper choice (you would be choosing a topper for the “wrong” reasons) but after you choose the most suitable topper for you if you still need to raise the height of the mattress further then I would consider using very firm polyfoam under the mattress because of the lower cost of polyfoam and because the deepest layers will have the least effect on the feel and performance of the mattress.
Phoenix