However! I was super-excited to learn that Big Dubs is now selling 'sleep suits' – aka, ONESIES! I'm not sure if there's a men's version, but the women's size 8-16 version is $19, as is the girls' size 8-16 version, and the girls' size 1-7 version is $17.88.
As far as onesies go they aren't the most practical. They only button down to the waist, so you'd have to undress completely to use the toilet. They also seem quite tight, which makes me wonder if they would pull awkwardly in the crotch if you're tall.
If you'd prefer regular flannel PJ pants, there are some jaunty polka-dot ones for $9.94, or various prints for $7.96.