Hi nyc runner,
As sas95 suggested … I wouldn’t make this assumption no. It will depend on the specifics of a mattress and what your testing indicates and you may well find that some mattress designs work well for both of you (see the first part of post #2 here).
I’m assuming that you’ve seen the New York list in post #2 here which includes the better options and possibilities I’m aware of in the NYC area (subject to the guidelines here) but your testing doesn’t indicate anything specific no (although a few of the stores on the list do sell split firmness mattresses).
If your careful testing indicates that they are both a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) then it would be strictly a preference choice yes.
Phoenix