Hi yoshi,
As you can see from post #1 here … the first steps in finding the best mattress is to exclude the worst choices (which it appears that you’ve done), some initial research about layering and materials (which it also appears that you’ve done) and then to research the best sources in your area and/or online (such as those listed in post #21 here) if necessary.
If you let me know the city or zip where you live I’d be happy to let you know of any better options I know of in your area.
From the looks of your “restrictions” and because you seem to prefer latex … you would be looking at a mattress that contained 6" - 7" of latex depending on the thickness of the quilting/ticking. 6" of latex would be much more common (because this is the thickness of most latex cores) and with a quilting layer (such as wool) you would finish out at about 7".
There may be a few options that have 7" of latex such as the Ikea here but the quilting in the mattress means that the finished mattress is closer to 8".
In most cases … this will be a single core where your choices are limited to soft, medium, or firm and either Dunlop or Talalay latex depending on the manufacturer. Some manufacturers may offer two 3" layers which would give you a little more flexibility in layering choices.
Since you are both lighter you will be able to get away with softer foams than someone who was heavier.
In a single 6" layer mattress … 100% natural Dunlop may make a good choice because it has a higher compression modulus which means that it gets firmer faster than a similar ILD/IFD (softness rating) of Talalay. This means that it can be softer with initial compression (for pressure relief) and yet firmer with deeper compression (for alignment) than the same ILD of Talalay which may make it more suitable for a wide range of sleeping positions. Dunlop also has a slightly softer side and a firmer side which can enhance this effect to different degrees (depending on the manufacturer of the Dunlop). In a mattress that had two 3" layers of Talalay … a softer 3" layer over a firmer 3" layer can approximate the same effect (softer with initial compression and firmer with deeper compression). Because there are so many variables involved … your own personal local testing (especially with the help of some good guidance) can be more accurate than what I call “theory at a distance” though so I would test both Talalay and Dunlop if they are available because they also have a different “feel”.
I think wool quilting would also be a good choice.
Phoenix