Tried a chin strap. No dice. Finally got a Mirage Quattro full face mask and was able to reduce the leaks to a reasonable level. Not too long ago I switched from a medium size to a small size, which is the right size for my face. Did this to aid in trying to control dry mouth. The medium was always pushing on my lower jaw towards opening.
Once I got through my adjustment period with my new, smaller Mirage Quattro my median leaks are always 0 and my 95% leak rate is quite low. I deo not have to readjust the headgear every night. I just put the mask on, fasten the lower straps, pull right and left on both sets of straps and lay down to go to sleep. After a while I will start to get a little leakage at my nose. I adjust it out with the nose bridge adjustment and then refit the strap tensions the next day.
The cushions do not require daily cleaning to prevent leaks although I do clean the skin on my face where the cushions touch nightly. In fact, sometimes I get lazy and do not clean the mask for quite a while. I just do not get leaks and I am a side sleeper although I do not try to bury my face in the pillow.
The short version of this is that the right full face mask is a lot better than I thought it would be based on my first experience with FFMs.
Full face masks may require more attention to getting the right mask and getting it fitted properly than others do and they do require more strap tension than other types of masks at the same pressure but they are actually quite good once one gets them squared away.
I will put my leakage rates up against anybodies. Not saying that mine are the best just that mine are in the same league with anyone with other types of masks and they stay that way with little effort.