The star made the comments after the press screening of 'The Pandorica Opens', when he was asked who came up with the jacket-and-bow-tie combination he has sported in the past series.
Smith said: "There are five or six of us involved in that process - I was involved. Actually I went to a costume fitting this very morning for next year, which was very interesting!
"I've just heard, basically, 'Tell him he can't have a hat unless it's written down that he has a hat!'. So let's see. There's going to be a whole back and forth now."
He added: "I've always said that I think it will evolve but I'm very pleased that the costume feels it has an element of the professor.
"But just practically, we film in November and it's freezing! And just a tweed jacket can get a bit cold, so who knows..."
Speaking earlier to DS, co-star Karen Gillan quipped that Amy Pond might sport a pair of boots when Doctor Who returns in 2011.