I think for this experiment, all I need is just food to start which would be even gentler.. one possible test I can use is just to see if my skin flakes less after eating a pack of seaweed a day. I don't use iodized salt, so with the exception of the occasional food purchase outside, I haven't been getting iodine from any source except milk because I don't cook fish at home (maybe I should).
Interesting point about fluoride and bromine, my water is both chlorinated and fluoridated. I don't have a problem with that, but if it's erasing the small amounts of iodine I got from milk, then this is interesting.
Mattresses are a big problem. Don't buy those smelly memory foam mattresses (especially the ones made by no-name Chinese manufacturers). You spend hours attached to it, so better to use regular closed cell foam or springs or something else. Another complication with mattresses is not just whether the material is one that likes to outgas like memory foam, but also all the flame retardants they add in case you are a moron who smokes cigarettes while lying in bed.
I will suggest that you crack your bedroom window open a little bit at night, even in the winter. It doesn't have to be a lot, even 1 CM is fine. It's just to get some fresher air coming in so you don't just sit there in stale air for hours.