Hi DSW61,
You can see some comments about the pros and cons of split layers in post #2 here.
It can vary based on body types and the weight differences between a couple, your sleeping positions and how closely together you sleep, and on the specific design of the mattress and the firmness of the layers but if you were to ask a large number of people that sleep on split layer mattresses where all the layers are split (including the top layer) you would find that a large majority would say no and a small minority would say yes (although it would be virtual sagging with weight on the mattress when they sleep in the middle rather than visible sagging).
With a solid layer on top of a split base layer the small minority would be smaller yet.
Phoenix