Had to go from back to side sleeper due to Degenerative Disk. Use CPAP since before issue. Several of the new "masks" are better for that - the nasal pillow kind.
I never had much luck with those special pillows, the ones with the contours for the mask, but some people swear by them.
Yeah, disturbing the mask can wake me, but I have to pee, anyway. That reduces the leakage - talk about ironic. Right now, my pads are enough, but I have to use briefs, not shorts. I do have acceptable reports from the machine about very little leakage.
That first wake-up on the machine was a revelation - it was so fine to not be tired to death! It improves your health, generally, if APNEA 's one of your problems.