I agree with YorkieRose ... they won't freeze, they find a way to be warm as long as there is a soft blanket, etc. available to them. Toto gets unusually cold [shivering] so she wears at least a little T-Shirt all the time. Usually little jammies at night and a little jogger or fleece jogger when we take her outside .... lately that's been rare!
Toto will scratch & burrow in her blankets until she is just right and gives a great big "sigh" ... then I'm certain she is warm.