I agree with continuing the long walks everyday. You can purchase a dog sweater and even boots for him or he may not even need them. One you get walking it may up his body temp to a more comfortable level. I know when I first start out a walk in the cold winter months I am a little chilly but warm up soon after moving.

How about a game you can play in the house? Hide & seak? Or if you have a long hallway like I do you can play fetch downt he hallway. (I just sit on the couch & throw the ball down the hallway, a very lazy way for me to exercise Kaige).

Even simple things like taking them along for a ride when you run errands or the like.