I made Annie a thermal shirt! She likes to layer it under her hooded sweatshirt.
Anyway, I just used an old navy thermal shirt that I don't wear anymore, shortened the sleeves, and sewed a seam so the front panel of the shirt was about half as wide, took up the shoulders (ended up being sort of a "Y" shaped seam on the underside) and that was about it.
She really likes it! I put it on her to try it on night and she started doing zoomies!! I couldn't get it off her so I just let her wear it to agility class. (I made her take it off after we got there though )