Hi!
I'm sorry for the loss of your Rottie, and happy you've got this new little one to keep you company. Please tell us a little more about your pup.
Yorkies do not have an undercoat like most dogs so they can be more sensitive to heat & cold. However, they are individuals and some can tolerate the different temps better then others. Gracie Ruth has very low tolerance to heat and I've yet to find a cold temp that she isn't happy in. Boo's just the opposite.
We keep our home in the low 60's at night in the winter. I've found if they are cold they'll just burrow under the covers and snuggle close to us. I often wake up to find 2 or 3 little heads poking out from under the covers between me and DH.
They are smart, they know where the warmest, coziest place in bed is.
Just watch how your pup acts, it'll let you know if it's cold or not. There are several YT vendors who make wonderful pj's that also work well when layered with coats to keep them warm when going outside. I'd suggest you invest in a tee-shirt or 2, a nice mid-weight sweater, a warm coat and a pair of pj's. That way you'll have them on hand if needed.