So, what I would do is book a supermarket delivery to your cottage, containing all the things you want to eat for your stay, from your supermarket of choice. I would reserve this as soon as Xmas delivery slots become available, as they sell out very quickly.
(Don't do what I did last year, book one and spend ages feeling all smug, before realising I hadn't actually checked out the order and consequently hadn't actually booked one at all).
In this order, for Christmas I would include one of those chickens you cook in a bag. They are lovely to eat and so, so easy - the timings they give you are always exactly right. And you can choose different options if seasonings.
I would also buy all the sides I wanted for Xmas dinner, preprepared, so that they come in foil trays and I just have to stick them in the oven. These would include:
Roast potatoes
Stuffing of some kind
Carrots of some kind
Pigs in blankets
Meddotersnean veg of some sort (missing it up a bit)
Maybe parsnips?
I would buy a tub of preprepared gravy.
I would also get a bag of frozen Yorkshire puddings which are dead easy, just stick them in the oven and they are done in about 5 minutes.
Maybe a bag of frozen creamed spinach too because I fucking love it, and all you have to do is melt it in a pan for about ,5 minutes.
I'd also buy a Christmas pudding to microwave, and a carton of cream and fuck loads of brandy butter.
In fact this is what I WILL do this year, if my plan comes together and I end up hosting.
It's so, so easy. And will be a lot cheaper than getting a ready prepared thing from a restaurant. And you will have flexibility to include yours and your family's preferences for sides.
I also think your partner and (depending on their ages) kids can help you with the minimum prep that is needed for a meal like this - basically staving cellophane with a fork, working out some timings and pressing some buttons.