Another idea is that instead of stuffing your drysack with clothes and rolling it to the ideal volume, you could just use air to make an air pillow. I tried this with two of my dry sacks. One of them (a super light one) would hiss out air from the roll top when the pressure of my head was on it, but my slightly heavier SealLine (77g for 10L sack) Storm sack seems to be air tight. The pillow did want to roll around a bit, but the comfort seemed to be good. You'd want a larger dry sack for this, as a small one (ie. 5L) feels like resting your head on a ball, whereas a larger one (ie. a longer one) does not. 10L is a good size.
I prefer to stuff mine with clothes, but on a cold night where you are wearing all your clothes this is a decent option.