We work with Hueber textbooks of in all of our German classes. The textbook Menschen is used in our A1, A2, and B1 courses. Sicher! is the textbook for our B2, and C1 courses.
Please make sure that you get these exact books (there’s another exercise book saying „HIER“ on the cover, but that’s the wrong one). You can buy the books in the Okerstr. 1 (U-Leinsetraße) at the bookshop Buchhafen or at Hugendubel and there are two nearby branches: One at Karstadt on Hermannplatz and another in the Neukölln Arcaden shopping center right by Rathaus Neukölln U-Bahn.