Hatice's Sapphire apartment is a real jewel - the view in particular, is to die for!

If you're not afraid of trekking up 5 flights of stairs and of the nearby school and its very frequent bell rings, then this is the place you should go for.
Location is great - just minutes away from dozens of lovely restaurants in Beyoglu - and public transportation to go and explore the city (ferry, funicular or tram) is nearby too. The neighborhood is fairly calm and friendly (of course, there is the call to prayer 6 times a day but that's part of the charms of Istanbul!).
The apartment itself is great: clean, spacious, light... and the view is, as said previously, a-ma-zing!
Hatice was a lovely host, very responsive and helpful; we were extremely grateful for her help in buying a museum card and arranging for a private shuttle to take us back to the airport.