Most likely you have many things to do today, and in the next few days, besides read. However, at some point you may happen to want to curl up with a fluffy robe, a roaring fire, a mug of hot chocolate, and a beautiful spaniel or two (or ten.) Substitute elements of the above with whatever comfortable Christmasy things appeal to you, and then add one Christmas-themed novel suitable for the occasion.
Christmas-themed mysteries are everywhere, and I like them very much. Teresa Romain has a whole set of Christmas-themed Regencies, for example. But Christmas-themed SFF are perhaps a touch harder to come by.
Fortunately, I don’t have to do the heavy lifting.
Here’s a list from B & N: 10 Holiday-Themed Science Fiction & Fantasy Novels. The list features Connie Willis, a Christmas ghost story by Paul Cornell that I just picked up to read because I really do like a themed story or two at this time of year, The Hogfather by Terry Pratchett — not my favorite of Pratchett’s work — and, good heavens, NOS4A2 by Joe Hill, what is that doing here? Well, it is Christmas themed, in a sense. I guess.
This list also includes a Sarah Addison Allen novel, which I don’t believe actually takes place during Christmas, but whatever, it is a lovely novel.
It doesn’t include, strangely, The Dark is Rising by Susan Collins, a classic, I would have thought. I’m sure you’ve all read that one. If not, well, seize your chance this Christmas and give it a try. Just start with The Dark is Rising; the prequel novel Under Sea Over Stone can certainly be put off till later. The entire story builds up to Christmas; the season is infused through everything that happens.
Now that I’ve thought of it, I might reread The Dark Is Rising myself this Christmas season.
Another very suitable fantasy novel for Christmas, but much larger: Winter’s Tale by Mark Helprin. Gorgeous, just gorgeous. Big, epic, beautiful, magical realism. Also, parts of it are kind of like distilled Christmas.

With or without spaniels and Christmas-themed novels, I hope you all have a lovely holiday! If you don’t celebrate Christmas, then I hope you at least find a chance to settle down with a wintry tale and hot chocolate.
Merry Christmas!