Hi Andrew R,
The only other mattresses I’m aware of that are customizable, and that use a combination of microcoils and latex comfort layers are Berkeley Ergonomic or the similar mattresses that are made by European Sleep Design. There is a list of the Berkeley Ergonomic dealers I’m aware of in post #12 here and European Sleep Design is in Folsom, CA.
There would be a much larger number of options if you either eliminate the ability to customize the mattress or the option of having microcoil comfort layers. There are some sources for innerspring/latex hybrids in post #2 here and the post it links to. Some of these may have some dealers in your area and some of them are also available online as well.
If you let me know your city or zip code I’d also be happy to let you know about any of the better options or possibilities I’m aware of in your area and some of these may also carry some mattresses that are “close enough” to your criteria that they may also be worth considering.
Phoenix