I stayed at Pinar's apartment in the Tarlabasi neighbourhood of Beyoglu for one month. The 1-bedroom apartment is spacious, clean and well maintained. The bed is firm, but comfortable and with radiators in every room it was sufficiently warm at night. (My stay was in the late fall, when the Istanbul weather is a little unpredictable.) The kitchen, though small, was perfect for cooking and Pinar provided nearly every kitchen item that one could need for meals small or large.
Contrary to what you might hear or read online, Tarlabasi is a safe and very interesting neighbourhood. It is very much a local area, where people live their lives, go to the local stores, drink tea for hours at the local shops, and go to the amazing and enormous Sunday market that is right on the same street as Pinar's building. It is very close to more touristy & fashionable areas (Istiklal Street, Galata, Taksim, Cihangir, Karakoy, etc.), but it is not a tourist area. So if you want a relatively quiet and relaxing place to stay, where you can see how "normal" people live in Istanbul, I'd highly recommend Pinar's apartment.
Pinar and Baran, her nephew who lives in the building, were extremely helpful and responsive to my queries. I would stay at Pinar's place again & recommend it for open-minded and thoughtful visitors to Istanbul.
Çok teşekkürler Pinar!