Hi jh10,
I think it may be helpful to start at the beginning again and “reset” your mattress search because some of your questions don’t have any “definitive” answers and are more a matter of deciding where in a range you may be rather than looking for more black and white answers which may not exist.
The first place I would start with any mattress search is post #1 here which has all the information, steps, and guildelines you will need to help you make good choices.
The issues of “safety” and “sensitivity” to different materials is very complex and relative to each person and “how safe is safe enough for me” is really a question that each person needs to answer for themselves because there are no definitive answers that apply to everyone (such as “should I use memory foam”). Everything is relative to each person’s sensitivities and preferences and their own “risk tolerance”. Post #2 here will give you some information and links that should be helpful in your research in this direction.
A forum search on MCS and on fibromyalgia (you can just click these) may also bring up some posts that may be helpful.
I would also keep in mind that there is no such thing as an “all memory foam” mattress. Memory foam is only used in the upper layers of a mattress and needs some type of firmer support layers underneath it (such as polyfoam which is most common or an innerspring).
I would also be very very careful about “ecofriendly” claims that are being made everywhere when they are only talking about polyfoam which is a petrochemical foam. You can read a little more in post #2 here. These claims are more about greenwashing for the most part and “ecofriendly” has little to do with “safety”. You can also read more about Saatva in this thread.
So I would start at the beginning and follow the steps one by one.
Phoenix