If you’re looking for solid accommodations in Mitte, I highly recommend Lux Eleven Mitte. Nice-sized rooms for Europe, full kitchenette (with cooking surface, but alas no pans), free laundry (including free soap, and coat hangers and baskets you may borrow), a lovely cafe opened until 11:30 pm nightly and a full-service restaurant. Wonderful, helpful, all-English-speaking staff. Not luxurious, but very comfortable for an extended stay and 3/10 mile from Alexanderplatz and steps from the Rosa Luxembourg Strasse Ubahn stop. Bike and scooter rentals abound.