Serçin warmly welcomed us with a turkish tea and gave us all the informations we needed, about the flat and the city. She gave us a list of adresses: what to visit, where to eat,.. Clearly we couldn't try them all, but the ones we try were fantastic!!
As for the flat, it's perfectly located, close to Taksim, in a beautiful district, 5 minutes away from the metro and tramway stations, next to plenty of nice bars and restaurant, and right in the middle of Modern Istanbul! It's also well-equiped with everything you need!
And Serçin, you've been the perfect host for us: every time we had some (mostly stupid) question (like "we forgot how to turn the WiFi modem on!") you've been very reactive and you stepped by with a solution!
So let's resume: great city, great flat, perfect host => if you want to really enjoy your stay in Istanbul, don't hesitate!!!