Inexspensive Health Spa'S In The South?

Im looking for a place to go as a last resort, no pun intended. I have severe psoriasis over 80% of my body and arthritis and am looking for a place to go to detox in the south, maybe Phuket or Koh Samui or that area. It would be nice if it were near a beach somewhere so I can swim and let the sun and water help my skin.

The short of it, I am looking for an all inclusive place where they will give me a place to sleep, look after me, feed me good things, and keep me away from the foods and other things that make my skin and joints suffer. A place like that in the USA will cost upwards of $500 per day, so I am looking for a cheaper alternative in Thailand, maybe for a month or two.