Isa's flat is well-situated in Beyoglu/Karakoy, a few blocks from artsy and trendy Cihangir. The flat itself is tastefully decorated, is quite spacious, and has a comfortable bed.
I spent most of my time outside of the flat but when it came to unwinding at the end of the day, I was very comfortable.
Isa doesn't speak much English, but he is incredibly friendly and warm. Definitely stay here if you have the choice!