I would say 'Lynx' but it hasn't got the same ring as when Marilyn said ... “What do I wear in bed? Why, Chanel No. 5, of course”
Absolutely nothing. I've been sleeping nude since I was ~6 years old. I've always felt that sleeping in pajamas or underwear felt too "restrictive", and I've always preferred to sleep in a cool environment (~65F ambient temp).
This time of year? Socks, flannel pajama bottoms, longsleeve T-shirt, and a sweatshirt. Summer, anything from in the buff to T-shirt and underwear.
Pajama bottoms and a polyester top that used to be for the gym. Socks too, & a sweatshirt during autumn and winter.