From my experience the sauna is fine but you are going to have to take additional sodium and electrolyte minerals. I think I said this but from my experience I do not think de-mineralization is good at any point for any purpose but am willing to be wrong. I just am willing to overindulge minerals ESPECIALLY when fasting :)
For me the benefit of a sauna is total ounces being sweated out not how much pain I experience in one sitting lol.
So... I tend to stay in for about 4x5-7 minute sessions with a shower rinse / pool inbetween. Once my pores are opened up I immediately keep sweating.
I enjoy using epson salt rubs and even bring a lemon or ACV spray to cleans my skin as well. Partly because it feels good and partly because it gives me something to do as I do not want to bring my phone for music in :)
I had never seen the boimetric bed but it looked awesome. I bought a tent like / IR sauna on craigslist for $100 and have used it for 5 years. it has been one of the best investments I have made but I would consider myself an avid sauna user! Half the time I go to the gym I skip deadlifts and just head straight to sweat