Hi Peanut,
I hope you don’t mind that I changed your post to a new thread to help others from Phoenix find the information more easily (there seem to be a few lately).
You are fortunate to live in Phoenix as there are some exceptionally high quality and value factory direct manufacturers there, 2 of which are members of this site. I also trust their advice and ability to help their customers find a mattress layering that is best for their needs and preferences.
Post #4 here should help a lot 
You are both on the slim side so I would be looking for a comfort layer in the range of 2-3" and in an ILD that relieves pressure in your testing (since you have the ability to test locally this will be more accurate than theory). Typically an ILD in a latex comfort layer in the range of 19 - 24 would work well. Because both of you are also stomach sleepers … then the thinnest firmest layer that relieves any pressure points on your side would also be best for stomach sleeping since stomach sleeping typically does well with a much thinner comfort layer and a firm support layer to prevent the hips from sinking in and causing lower back pain due to sleeping in a swayback position.
So the options I would be looking at would be about 2" of 19 - 24 (towards the low end) latex over about a 28 ILD support core or 3" of 24 ILD latex over a slightly firmer support core (in the 30’s). If the support core has a middle and lower layer … then the lower layer can be even firmer. Pay particular attention when testing for pressure relief to do so while completely relaxed on your sides and make sure you don’t feel any pressure in your hips, pelvic crest, or shoulders. When you are testing for alignment, make sure you test on your stomach as well as side to make sure your hips aren’t sinking in too far on your stomach and your shoulders are sinking in far enough on your side. Again, the thinnest firmest comfort layer that is pressure relieving on your side and allows your shoulders to sink in enough would be best for your stomach sleeping.
If you find that your individual needs are too different … then a side by side split with each side customized to each of you is available from both of our members at no extra cost.
Also make sure that if you end up purchasing from either of them to let them know you are a member here (which is automatic with a post in the forum) as this entitles you to an additional 5% discount from any manufacturing member of the site.
Hope this helps, and I’d love to hear how you make out.
Phoenix