So I decided to some research on my own and my studies reveal that the doggie jacket is not a good idea. Look at this article from a reputable journalistic source:
"wearing a coat can be very dangerous for a dog, especially if it’s a heavy coat . . . Just because we [humans] feel cold, it doesn’t mean our dogs do . . .”
I'd like to pose this question to my sister, who is such an advocate of the jacket: if it's so good for me, why do you see me running away when you pick it up to put on me?