With the cost of clothes, I feel it is best to scrimp first on the clothes no one sees you in. This excludes your spouse, of course, who will only care that you're soft and warm!
I buy men's heavyweight crew neck undershirts in size L - "large/tall". They cover my rear, but are small enough around my neck that my collarbones are covered. Then I buy pink dye for a buck and color them in my washer. I have a feminine cozy look that's still comfortable and cheap!