Hi railit,
The industry has changed a lot in the last 12 years (and not for the better unfortunately).
There are still many smaller manufacturers that are sold either factory direct or through better sleep shops that are still providing great quality and value but they are usually drowned out by the massive advertising of the major brands and chain stores which don’t sell mattresses with the same quality materials as they did one or two decades ago.
It seems to me that you have already tried the most likely suggestions and hopefully the next little while will solve your odor problem and symptoms. At least your experience with Simmons showed that you don’t have the same issue with every type of memory foam.
I also had an issue with a specific type of memory foam (as you can read here) and this was the only time I’ve reacted to any memory foam that I’ve tried. Hopefully this is a unique circumstance for you as well.
Phoenix