Welcome, Puff! If you go to the top of this page to the "Digitrad and Forum search" and type in "winter solstice" (without quotes) you will find many threads on this topic, with many wonderful songs.
My group has performed a number of winter solstice songs as well. My dear friend Alouette Iselin has written three that I do every year, and I'd be happy to share them with you if you PM me (to find out how to do that, go to the Mudcat FAQs at the top of the thread list!).