Highly recommend Yusuf’s flat. We tested his patience by arriving horribly late but he received us personally with a smile on his face. Location of the apartment couldn’t be better - right next to Karakoy tram (at the end of the Galata bridge) so we had Karakoy, Galata and Istikal all on our doorstep for dinners.
We had the most amazing fish wraps at Balik Durum Mehmet Usta (5 mins max), loved the restaurant downstairs for lunch/dinner (Restaurant Gumruk) and our two fave local breakfast places were Muhat Muhallebicisi (around the corner by the tram - super friendly and delicious) and the bakery Koskeroglu.
The tunel was very convenient to get up to Istikal street and we adored Pera Anyaka.
On the first day we happily walked over the Galata bridge and all around Sultanahmet, but it was very handy to hop on the T1 tram which takes to all the top sights in moments. Buses then take you up the Bosporous, or the ferry behind the flat goes over to Kadikoy. Do invest in an Istanbultkart for convenience of using the local transport.
The flat itself was very comfortable - wifi was reliable and there was a tv with access to Netflix. Beds were comfortable. There were a few hangers to hang up essentials/shelves and a fridge. There was also a washing machine which was handy for our week-long stay. Overall we highly recommend.