Hi Meliblue,
The first place I would start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you make the best possible choice that meets all your criteria (including motion isolation) … and know how and why to avoid the worst ones.
Memory foam is the best at motion isolation but latex and pocket coils are good for this as well. The best way to test for motion isolation though is your own testing on a mattress using the testing guidelines in the tutorial post (with both of you on the mattress) because a mattress that may be “motion isolating enough” for one couple may not be as suitable for another couple that is more sensitive.
Once you reach step 3 in the tutorial then the better options and possibilities I’m aware of in the Olympia area (subject to the guidelines here) are listed in post #5 here but it sounds like you hope to purchase a mattress before you move so if you let me know your current city or zip code I’d also be happy to let you know about the better options or possibilities I’m aware of in your current location.
The tutorial post also includes several links to lists of some of the better online options I’m aware of as well if you are considering making an online purchase.
Phoenix