Yes! It's true, there IS a footed sleeper for your character, it's called the 'Blast off pyjamas'.
Made me grin. Footed sleeper with one of those diaper flaps on it. It can be reverse pick pocketed from Bumble in Little Lamplight (Provided you didn't kidnap her for the Slavers. Bet Karma is really biting you in the ass now, huh?)
To do this, if you're unfamiliar with reverse pickpocketing, you need to go into sneak mode, be undetected and go into the pick pocket menu. Now that you're in it, instead of taking from the character, you instead want to GIVE them something that replaces what they usually equip, in this case, I used Pre-War Park Stroller outfit (So she'd still look cute.) as to get her to unequip the pajamas. Once you have successfully achieved this without being caught. Save.
Now. Exit the cell you're in (That's game speak for 'The room' you're in, but sometimes a cell can incorporate several rooms) and then re-enter. Now, Bumble SHOULD have unequipped her PJs and put on the outfit you gave her. Save again. Now, back to normal pick-pocketing. Take the Blast Off Pyjamas from her, and bam, you have a footed sleeper. Enjoy. It's no good for armor rating and gives no boosts but I figure you won't want it for a 'permanent armor' anyways!
Happy jammie wearing!
Blast Off Pajamas - Fallout Wiki - The Vault