DS had a grobag in his big boy bed... up until around 2.5yo I think, he was able to walk around in it fine! He transitioned out of it during the summer, cause in Bris, summer nights can be just too hot for anything...
I dont remember having an issue with it at all come the next colder months when he bagan using a doona. The only frustrating thing was him kicking it off and getting cold lol.