I would highly reccomend to stay with Volker! His appartement is super nice, great location - quiet, but super central. It's close to Ubahn so you can go anywhere easily. The apartment was very, very clean and the bed is super comfortable. There is a kind og closed off private balcony, where it is possible to open and close the windows.
Furthermore Volker is simply extremly kind, and he was sincerely concerned with giving us a nice stay and good recomendations for tings to see, places to go and good restaurants.