Are you asking this because of Stranger Things?
I think the biggest issue is that a bathtub isn’t big enough for most people to float in without touching the sides. Assuming the tub is large enough, the epsom salt would work to make you float and would be cost effective. You would have to figure out a way to regulate the temperature to 98.6 degrees though. And you would have to be in a pitch dark room.
Yeah that sounds nice. But what if you just ended up spending all of your time in the tank? It might be too much power to have a tank like that on tap