Hi jwjojo,
Yes, you already know the answer. 
There are too many unknowns, variables, and personal preferences involved in choosing a mattress for someone else to make specific suggestions based on specs (either yours or a mattress) or theory at a distance that can possible be more accurate than your own careful and objective testing (using the testing guidelines in the tutorial post) which is always the most reliable way to predict which mattress will be the best match for you in terms of PPP (see mattress firmness/comfort levels in post #2 here).
If you’re also considering a new foundation, you may need to order a split queen version to accommodate your stairway issue.
Phoenix