Not doing this this year... but previously when it's just been me, exP and kids or just me and kids:
Had special Xmas breakfast and opened presents.
We live near some lovely coastline, so have all bundled up and gone out for a lovely Xmas walk by the sea, one year it snowed as we got there and it was lovely and Xmassy to be the only people out on the beach and walking in the woods nearby.
Got everyone involved in getting the food ready and in, so that when we got back from our freezing walk, the meat was almost done and veg all pre chopped and ready to go on to cook.
A great family film was pre selected to be watched while the food finished cooking, Harry Potter or similar.
After Xmas dinner, all snuggle under blankets near the fire, lights out except tree lights and all watch the Dr Who (or similar) special Xmas episode together.
Whenever we've done that it has been quiet but felt very special, just us having a lovely quiet day. Getting lots of fresh air in the middle really worked to tire the kids out, provide excitement and if we bumped into anyone else they were always very friendly and happy to chat to us, which helped the atmosphere too.
Much nicer than having a big house full, or having to travel over to relatives' houses tbh.