This may be one of the weirder things about me. It originated from having a very aggressive cat who would find my appendages in the night and a) would try to get me to pet him or b) would attack any twitching hands and feet c) he'd sleep on my kneecaps, which was uncomfortable... So based on when I got that cat and when he was at his weirdest, I've been sleeping this way for more than 10 years.
Step 1- While laying on my back, I rotate my shoulders backwards
Step 2- I put my palms on the mattress and then slide them under my legs, just under my butt
Step 3- I cross my legs at the knees, like I was sitting Indian-style
I call this "The Boxing Helena". It is impenetrable to cats.
I wasn't bouncy enough to be able to sleep this way while I was pregnant and it nearly drove me insane.