Hi Sheina,
I am not an expert on the warmth factor as I usually layer but I just ordered 3 sweaters from Becky (a YT member - My Sophia) that are just adorable and very reasonably priced. Here is a link to the thread that I heard about them from.
http://www.yorkietalk.com/forums/yt-seller-feedback-seller-reviews/190445-thank-you-so-much-my-sophia.html
Becky was wonderful, has made them to order and even did one that will match Zoey's carrier perfectly! Maybe give her a pm and see?
Good luck!
Attaching pic of the ones we are getting... two like I had seen but with ruffles and then the one special to match the carrier. Becky is really terrific!
Red leopard.jpg