Anything you think looks comfortable and warm. Sweaters are nice. I have a friend that makes turtle necks out of tube socks. I mainly have hoodies for my little Yorkie and Maltese. I also let their hair grow out more in the winter months. They love the snow but they shiver their poor little rear ends off and if they don't have something on the snow forms snowballs on their bellies that are almost impossible to get off!