We really enjoyed Koray's studio in Istanbul. Great for one person or a couple, it has everything you need.
We spent two weeks working remotely from the apartment, internet speed is good, the kitchen is well equipped to get by for a short stay, the bed is comfortable and the windows are sound proof making it perfect to focus.
The location is amazing, walking distance from all the major destinations in Beyoglu, right across the Tophane tram station and a 2 min walk from the Karakoy ferry station. There's also grocery stores, and everything you need nearby. We really enjoyed the spot.
Finally, Koray is of great help and always available! We have a home away from home :)