This AirBnB was by far the best deal we found around Istanbul Center area. For the good price you get a stylish appartment, very clean, new amenities, and a 24h-reception which makes you feel extra safe (as Istanbul city can feel a bit scary in the first nights).
Please be aware, that you should be able to walk stairs to your floor (1-5, or 6 for penthouse). The friendly reception would help with your luggage.
Each floor has two appartments (except penthouse), and even if the walls are not superthick, we never heard the neighbours.
Overall, we 100% recommend booking this place :)