Hi OP,
You don’t have to have a huge family around to have a great Christmas and start some traditions! Here are some of the things I did as a child, do now and would have done if I’d been in my DSDs life when she was younger:
Run up to Christmas
Make some Christmas cards. Can be potato printed penguins, feet turned into reindeer with googly eyes, whatever. You do this every year (it’s tradition!)
If you can, each of you take your DS to buy the other one a gift. Can be somewhere like B&M and for a tiny amount, important thing is that your DS chooses it and wraps it.
My parents would take us for a drive in the evening and look at all the Christmas decs in town and in people’s houses. Something exciting about wrapping up and going out at night.
Start building up an advent calendar of Christmas books. If you already have some, wrap them up and open and read a new one every evening.
Christmas Eve - Go out! Sometimes it would be for a drink and cake, sometimes a meal (depending on finances). Go home, early bath and pjs, Christmas Eve box if you want one and watch a movie together. We watch the same ones every year.
Sprinkle some reindeer food outside (bored seed and edible glitter!).
Put carrot, milk and mince pie for Santa and Rudolph, quick check to see that he’s on his way!
Must do - read a Night Before Christmas with just a candle for extra excitement. Early(ish) bed, so you can both do all the veg prep etc for the next day, and set up your living room (or wherever you open presents)…
sprinkle some icing sugar (snow) and get some large shoes to make Santa’s footprints. Put some extra fairy lights up. If you can, when you know you don’t have to go in that room again, seal up the door with wrapping paper which your DS will love crashing through in the morning!
Christmas Day - what YOU choose! I would go with some presents, then one of you goes for a walk with DS while the other does the food stuff. Local park is great if you can, DS will have lots of swings etc to himself and will love shouting Merry Christmas to everyone. Back home, play with toys.
Lunch, lots of crackers, Christmas movie…
Boxing Day - if DS has lots of gifts I would spread them out over here too. Then dressing up in smart clothes, it’s time for a kitchen disco!
not sure if these are to your taste, OP, but hopefully some fun ideas that you can do every year and start some lovely traditions.