We had an excellent time in Julia's and Tarkan's apartment. It is beautiful, furnished with luxury furniture, the bathrooms are beautiful (+ very comfortable beds, beautiful linens, nice carpets, etc.). There is also a very modern kitchen with all necessary equipment and a good AC system. The place is beautiful, cosy and very clean (just maybe a lack of daylight as it is on the 2nd floor of a narrow street).
The location is I think the best you can have in town, a few meters from Galata tower.
Julia was very easy to reach and her colleague who welcomed us was extremely kind and available for any question. She also proposed tips to visit the city and the historical Galata neighborhood. In short, if light is not a problem, I can only recommend this excellent address and these extremely nice hosts.