OnePiece - Jump in | One Piece, Jumpsuit, All-in-one, Onesie, Chilloutsuit
I guess these are becoming popular especially in the uk. they are like sleepers but feetless and with hoods. they are made by a norwegian company and are quite expensive but they look amazingly cute...
this is the link to an article about them in the guardian:
Zip up, look sharp: the OnePiece roadtested | Life and style | The Guardian
and here is a sample picture: