Side sleeper here. I put one thin one between my legs so they are parallel and the joints don’t press against each other. I have a thick “hugger” so my top arm doesn’t just hang unsupported and pull on my back muscles all night. The problem is my lower arm gets pressed on all night or I have to find the magic position for it that is comfortable.
Back sleeping means I have to get the neck just right but then I usually snore and I get wacked by my wife.