Are there any Christmas Morning gatherings near you that are interesting to you? The main types that come to me are:
Church services (your own or another faith)
Swim
Run
I would definitely think about what treats are special for you to enjoy - a nice dinner (probably either one that you will enjoy taking time to cook, or that is super easy to do, my money would be on spending time doing something special). But also a lovely breakfast (fresh coffee in a cafetiere, freshly baked pastry, and nice yoghurt - or a full on smoked salmon on a bagel with poached egg and hollandaise sauce....) and lots of lovely snacks to pick at.
If you do drink alcohol, it is worth having a buck's fizz for breakfast on 25th (just get a bottle of bubbles that holds 1 glass unless you want more later, then get a larger size), and a bottle of something really special to enjoy sipping throughout the day or that would go really well with your dinner?
A larger dinner could be fine if it is the kind that you will have leftovers to use in something else - I am quite happy to make a proper roast for 1 as I will only do enough potatoes and veg for that meal, but I have loads of uses for leftover meat, both hot and cold. And I can freeze leftover meat as well to use another time. I often make soup with leftover veggies, or homefries with roast potatoes, or a bubble and squeak type dish or top a shepherd's/chicken & mushroom/smoked fish & brocolli type pie with mash etc.
I love to read but don't get a lot of time, so often have a new book and a stack of books I haven't got to yet for Christmas. And a new puzzle book (sudokus, wordsearches, logic problems, crosswords etc). Sometimes I have a good magazine to flick through (women's interests ones like Good Housekeeping, Good Food etc, but it could also be one on sailing, computers, current affairs, crafts, ....just whatever looks good in the shop when I am looking).
If all your friends with families are around, can you organise a gathering involving them - maybe making decorations or decorating cookies before Christmas, or just games and nibbles one of the quieter days afterwards - where you are making it about the DCs getting together and doing something, which allows the adults some quiet relaxed time to catch up with each other. Maybe outdoor games and a winter picnic in the park (sausage rolls and cookies to eat, and hot choc from flasks perhaps) if you can't accomodate in your house?
Set up a playlist of music that you will enjoy, and of things to stream or watch that you can just turn on and relax with. Have a lovely candle with a fragrance that you like to light.
And if the time that makes you less happy to be alone is talking to family all together, can you organise to do that at a different time - before they are all together (and spreads it out a bit too), or just before you yourself go out to do the Santa Run locally, that kind of thing? Maybe save something that you know they will also be having or something you are looking forward to enjoying, ready to eat/drink/listen to etc, straight after the call? Or do it just before you get stuck into preparing food so that you will be busy (and can take it out on peeling the poor carrots or blame the strong onions for any tears if you need to)?