I stayed with Fatma for many weeks in December 2013, in the attic room on my own, and then with my boyfriend in the larger double room, and had an amazing time.
The neighbourhood, Tarlabaşı, is different and more down to earth than the posher neighbourhoods around. The location is wonderful: it's easy to get anywhere by foot, taxi, bus, dolmus, metro or boat.
Fatma, who lives there, and her daughter Elvan, who lives in Italy but is quick to communicate by email, are extremely friendly and helpful.
Fatma also cooks wonderfully and even offers cooking classes.
I would definitely recommend staying there, for three nights or three months, and hope to stay there again myself.
Be aware though that if you have respiratory issues, this might not be a good choice as there is a fair amount of smoking happening inside, and even the neighbourhood is quite smoky because of the coal heating.