I was diagnosed with PD one year ago. My husband and I bought a Tempur-pedic last May due to the back issues I was having. We bought a king-size mattress to replace our old mattress set. I also do not have problems with turning over in bed at this point. But I've heard that if that does become an issue that sleeping on silky or satin sheets AND wearing a like fabic in your night clothes help with the issue of turning over in bed. (I wonder if you have to be careful of sliding right out of bed?)
One point you might want to be aware of with Tempur-pedic beds.....if you get warm when you sleep, you will really get warm while sleeping on a Tempur-pedic. My husband got SO hot that he couldn't sleep on the T-P mattress so we had to return the king-size and get an extra-long twin Tempur-pedic for me and an extra-long regular mattress for him.
Personally, I LOVE my T-P mattress. My whole body just gives a big sigh of relief when I get into bed!Good luck!