Like someone else mentioned, assuming you finish on 21st:
Over that weekend, there will be lots happening - church events (carol concerts etc), carolers in town, movies, gigs in pubs etc.
And still lots of last minute shopping etc.
So I would get out and about a bit those few days, to enjoy the atmosphere at least - meander around the city, even if not religious, pop into a church for the peace, stop for mince pies/coffee and people watching etc. Maybe grab a bargain if you see it, like the last minute over-stocked turkey joints or posh nibbles...
And yes, to getting the house as you'd like it. Decorating. Cleaning. Making it cosy, having nice blankets/rugs washed to snuggle into, logs for the fire or fuel for the heating, clean sheets for the bed.
Have things in for a few days peacefulness - nice candles, good movies/box set/books/music, relaxing bubble bath/shower gel (even a mini spa?), and good food that YOU would enjoy that is either really easy to prepare or something you can get stuck into (enjoyably).
You say your friends will be very busy beforehand - but would they like to meet up later on? Could you arrange either an outing (meal, hike, pub, gig, movie, ....) or host something in your place after 25th on a date that works for them too? You'll have time to prep for it, and they will enjoy it more if not pressed into it when they are manic beforehand, but may even welcome it to fill a gap after 25th before everyone heads back to work/school etc.
And perhaps think about getting out into the outdoors yourself as well - a decent hike if weather is ok, walk in a local park, visit some museums or galleries or heritage sites etc once they reopen?
Or maybe take the time to learn a new skill - with a block of 2 weeks, even taking Christmas itself into account, a few days working on a project or a skill could keep you quite usefully occupied.
Is it worth considering a good declutter, or restocking the fridge/freezer etc in that "after" period also? Particularly the freezer, with meals for once you are back at work - hearty healthy ones to get through the icky days of winter.
And yes, if you have the budget, a short trip within the UK or farther afield could be something to look forward to after 25th and before returning to work.
Hopefully there's something there to whet your appetite!