Hi GinGin,
I switched your posts and my reply to a new topic of its own.
Latex toppers are quite heavy and floppy and generally stay in place well on a mattress … especially with a mattress protector and sheets on top of them which would also help to keep them in place … but you could test the split topper when they get the firmer one in to see how you feel about the different firmness levels on each side and the transition in the middle or whether you would prefer a single firmness topper like the one you tested in the store.
There are also component mattresses available in the Detroit area where you can choose split layering with different firmness levels on each side of the mattress for couples who have different needs and preferences similar to a split topper but the split layers would be inside the mattress cover.
Phoenix