The appartment was perfect! Clean, cosy, with everything you would need, perfect location: in a quite area, but very close to the central street, just 4 mins away from the underground station. I would live long-term in that kind of appartment.
I am also very grateful to Hasan, who made our stay incredible. He was nice, friendly and very helpful. He organized the transfer from the airport, recommended to us all the nice places in Istanbul: sights, restaurants, etc, explained to us how to get a ferry, an istanbul card and so on, gave some info on Turkey as a whole. Thank you very much!