These days, most people stay in holiday flats in Berlin. It's much cheaper and you don't have to do the full week. If you're interested, I'll see if I can find a website in English. But it looks like you really want a hotel.
My DS3 has been studying in Berlin for the past 5 years but I am ashamed to say we haven't been to visit him once.
Last time we stayed in a hotel there it was way out in Teltow on the outskirts, so, sorry, no personal recommendations.
Go with a chain you know and trust, rather than looking at tripadvisor et al. Hotel reviews by punters are all so ridiculously exaggerated and usually contradict each other. Pick the criteria that count for you*, and go on that - just work with the facts!
* Such as : breakfast included, free wifi, situated near the station, bar, pool, safe in room, baggage storage if you are leaving later in the day after checkout, free shuttle, bicycle hire.
Enjoy your trip!