One suggestion is to find the same kind of upholstery warehouse that you found in California.

One way is to head to a library near you that has "Yellow Pages" books for large communities near you. Look in the "U" section for upholstery, upholstery supplies, upholstery fabrics and begin making phone calls.

You probably need to have her along to test the materials for desired comfort.

You could also just call one of the many suppliers you have found online and talk to them. You will be at a disadvantage because you have no recollection of any of the technical specifications of the old foam that worked well.

With enough telephone calls, polite ones, you will gain a lot of information and probably find someone reasonably near you to go visit and test for suitability. Your wife will likely have to make that decision in person.

If you have custom boat makers nearby, they probably make mattresses for sleep-in boats, for example, or RV builders or sales, ...

You could also look up "Foam" in the yellow pages. I found a local supplier that way. Haven't called to see what they got, though. Holiday today.