Looking for a Room and Nice Flatmate(s) Close to Checkpoint Charlie (Moving from Italy)

Hi!
I will move from Italy to Berlin for a paid internship from the end of august till the end of December. My workplace will be close to Checkpoint Charlie and I am looking for room in an apartment (I need anmeldung) close to that area. I would like to have a sunny room with a double bed and a desk to work from home. My Girlfriend will visit me from time to time for a couple of days (she lives in Italy) and I would like her to be able to stay in my room comfortably.

I am a computer science PhD student which enjoys a good nerdy evening filled with games and tv shows as well as working out (better if not alone). Currently I am practicing mixed martial arts, but I also like going to the gym, working out outside, and playing team sports like ultimate frisbee (which i recently discovered). I also like to talk in front of a beer in pubs and rarely even clubbing.

Having a flatmate (or flatmates) sharing some of the aforementioned passions will be of course a plus.