keep wearing them. You never know when you will meet your next guy, and he'll appreciate the effort you made with the underwear
I'm going to walk around in my underwear, buy some new underwear, and even have an entire party in our underwear! What a celebration! It's so much more comfortable being in your underwear anyways - so why not party in your underwear?!
L.L. Bean makes cozy ones for winter. But I'm sure you could get nice stuff at a department store sleepwear section, like Macy's or JC Penney. I don't know of any sleepwear/ lingerie stores that target older women only.