My DS used to get out of bed to play, and then just fall asleep near where he was playing. After awhile though, we started to find him back in his bed - guess he cottoned on!
Just dress him warmly enough (took mine awhile to figure out he could burrow under the covers), and maybe lift him into bed if you find him asleep on the floor before you head to bed - that way it might reinforce the 'bed is for sleeping' thing if he wakes up in bed.
He also had his kiddy couch in the bedroom that he slept on sometimes - it doesn't concern me too much as long as he's warm - if he's asleep, I don't care where it is!