Madrid is a great city with loads to see and do, the metro is excellent and easy to get around.
I've been there a few times but never managed to get to see a game at the Bernabéu - yet!. My lad did the stadium tour and can recommend it especially if you can't get to a live game, it costs about £30.
Not many home games in December though:
Sunday 1st - Getafe
Sunday 22nd - Sevilla
https://www.realmadrid.com/en-US/ti...neral&filter-football=primer-equipo-masculino
I've been to games at Barcelona and Valencia and got tickets via the club web site / at the club ticket office.
I still get emails from Barca as they see me as a loyal fan

Do it yourself flight, hotel and tickets will be a lot cheaper.