Hello,
I certainly understand your desire to have a chemical free mattress. While PBDE’s are no longer used, many other chemicals still are.
Latex as you mentioned is definately more durable than other foams and because it can be made in a wide range of firmness/softness options it can be used in both comfort and support layers. The RoomandBoard mattresses you were testing are made with Dunlop latex which doesn’t have the same range of softness options as Talalay latex but both can be very high quality materials.
There is some very good quality and value available in the LA area which means that the uncertainty of a DIY mattress would not be necessary. When possible … it is always more accurate to test a mattress locally and then purchase the same mattress that you have tested if the value warrants it rather than taking on the variables in “duplicating” a mattress you have tested.
There is a list of Los Angeles manufacturers in this thread. The first place I would visit is Flexus Comfort. They are a manufacturing member of The Mattress Underground which means that if you register on the forum and make a single post under your username … you will be entitled to an additional 5% discount for any mattress you purchase. All you would have to do is tell them you are a member and your username on the forum.
In terms of fitting a mattress to your specs … Flexus is good at this and can also do a side to side split if your needs are different. You may for example need slightly softer foam to achieve good pressure relief because of your lower weight. Of course actual mattress testing and preferences also plays a role here and is always more accurate than “theory at a distance”. Side sleepers typically need slightly thicker/softer comfort layers than other positions to accommodate their pressure relief needs. In your cases (both of you), the thinnest comfort layer that worked well for your side sleeping would be best for alignment when you are on your back. This would likely mean a comfort layer in the range of 2-3" depending on the firmness of the support layers underneath it. Most of the “firmness” that people feel on their mattress (and the ability to support the heavier parts of your body and keep you in alignment) comes from the deeper support layers under the comfort layer and the comfort layers are the part that provides the pressure relief. In other words a mattress needs to have a combination of both softness and firmness in the different layers.
Encased coils certainly reduce motion transfer but so does latex and even polyfoam in the support core of a mattress. Most motion transfer comes from non pocket coil innersprings in a mattress.
For most people … the value at Flexus and other factory direct manufacturers would certainly be better than RoomandBoard using the same or better quality materials.
Phoenix