The reason that I wear snug pajamas or trackie bottoms and t shirt is because if I wake up in the middle of the night I don't get any cold spots like shoulders or arms and it is easier to get back off to sleep. Also I prefer pajama trousers completely covering my legs as I tend to get attacks of cramp if the cold get into my calves or feet. If my legs are uncovered I seem to be more prone to cramp. Nighties are not much help because the legs still get chilled. There is nothing worse than hopping around the room naked and screaming in the early hours.