I prefer to sleep naked because it has taught my body to regulate its temperature better. Since sleeping naked, anytime I get a bit cold, my body automatically heats itself up, which is really helpful when being outside. I have learned to sleep Naked 365 days a year, INCLUDING WINTER!!
It depends really, I mainly would say that I sleep naked but other times I will wear a nightie and knickers. If I am abroad in a hot country like Spain etc then I will either sleep naked or wear a swimsuit (one piece) to sleep.