I found a great travel winter jacket: Uniqlo’s Premium Down Ultra Light Parka.
For Men, Women & Children (but children’s are only for sale in Japan..I know, it’s a pitty)
It’s so light it will fit under any other coat, in any suitcase. It’s so compact it neatly folds into a little travel bag, matching the many colors available of the jacket. It’s a good price too at 60pounds (about 100US$ but I cant find it on the USA website for Uniqlo for some reason…).