Made for low maintenance people Union Suit Pajamas are pretty much da bomb as far as winter PJs go. They don't pull up when you're sleeping. You stay warm and cozy from neck to ankle AND when you roll out of bed in the morning you just throw on a skirt or some jeans and you're ready for the day.
Plus Mod Unions don't have any fasteners making them extra delightful to sleep in (for those princess and the pea types) because there's no hard metal zipper head or plastic buttons digging into you while you are quietly slumbering.