We had a very pleasant overnight stay at Christina & Helga's place. The place was very clean and big for two people! You'll have the whole attic by yourselves, there's a private bathroom with towels and toiletries available. There's also free coffee / tea and biscuits in the room!
The check-in process is smooth and you can do self check-in.
It's just a 5 minute walk away from the train station and the neighbourhood was quiet. The train ride going to Berlin central station takes approx. 30min.
We'll definitely book this place again when we visit Berlin