I agree with you, it must be very disappointing you had found something that helped with your sleep and now it is not available. It sounds like you have tried to replicate it at home with a bath of Epsom salts. Most baths are not long enough to get all of you wet at the same time!
Either your knees are out in the cold, your feet, or you are twisted up like a pretzel!
Are there other ways you could create the softness of the flotation tank?
Do you have some soft quilts you could pile up, lay under a blanket to keep yourself warm, put on some calming music, do some calming breathing and tell yourself you are relaxing. Sometimes we can trick our minds into thinking they are somewhere else like a floatation centre.
What about a blow up mattress? Put a soft quilt on that.
Yesterday I went for a 13 kilometre walk hoping that would assist me in sleeping through sheer exhaustion. Didn't make a difference to my sleeping, but I had plenty of exercise and saw streets and roads in our region I'd not been on before.
Wish I had the answers for you!
Cheers from Dools