You absolutely can sleep with only a comforter if that’s what helps you sleep well at night. This is even the basic idea behind a duvet, which is thicker than the traditional comforter because it’s meant to replace your other bedding. You might want to purchase a separate cover for your comforter to stretch out the time between washings. Otherwise, you’ll have to throw your comforter in a washing machine about once a week to keep it clean.