I also have a mummy sleeping bag, especially in cold weather.
To be honest, I toss and turn and the bag just does its own thing. My biggest issue is that I’m a stomach sleeper, and I also like to use my arms as a pillow.
So I always end up kinda slithering my way out of the top half of my bag. So, I usually get extra long sleeping bags so I can kinda sink down inside it.
But yes, the struggle. Struggle struggle.