We do a lot of trips so I'm hopeful qualified to reply!
Last year took my husband to Cornwall for 3 nights, and London for 2 nights, as short UK breaks, and we did 2 nights in Barcelona and 2 in Bruges as abroad.
This year we did 3 nights in Edinburgh, 3 nights in Devon, and 2 nights in Oxfordshire for the UK, and I didn't do a mini break abroad together with my husband this year, but I did do 2 nights in Amsterdam with my son, and 2 in Paris with my daughter.
Favourites for short breaks have been Oxfordshire as we were close to The Cotswolds- one of my favourite places in the UK, London- because there's SO MUCH to do there, and do much is free (we're museum people), and abroad, Belgium, and the Netherlands are both so great for short breaks.
I also adore Norway, Sweden, Denmark, and Finland for any length of break, but a. I'm biased as I speak the languages so they always feel like easy countries to do, and b. In March.... if you're not a Winterling like me, you might not enjoy so much, as it is PAINFULLY cold....
Wherever you pick, hope you have a fantastic time! And also a wonderful Christmas!