I just brought two footed sleepers from Footedpajamas.com this morning at $19.99 each! I figured it was a great deal and I'd posted it up here as soon as I got home from work.
Most of the site is on sale for $19.99, but they also have some "Cotton" ones which have their version of the non-slip soles for $24.99.
I will warn you though, they only ship FEDEX or UPS and the cheapest is $17 for five day shipping.
Footed Pajamas | One Piece - Adult Footed Pajamas, Kids Footed Pajamas, Toddler Footie Pajamas, Infant Footie Pjs