If you're looking for somewhere quiet, outside of the more touristic places, and cozy enough to spend a medium to long stay, I think you'll love Eyüp's place :) We stayed a bit over two weeks and felt at home pretty quickly
It's great, well decorated and comfy. Everything you need should be there.
The kitchen is absolutely perfect if you want to cook a little, with the oven and the stove with four burners. There's no microwave, but we didn't need one personally.
The easy access to the outside terrace (shared with the floor but very quiet) was lovely too!
It's very close to the mall (5 minutes going down some stairs), which was very handy, but you also have a couple of small grocery stores just 2 minutes around the apartment.
If you want to grab a bite, walk on the shore, or take the ferry or Marmaray train, it's about 10 to 15 minutes going down from the apartment, and there's just everything really close-by! Plus, if you don't feel like going out, delivery services are very efficient too :)
Be mindful that this is, overall, not a touristic area, which means you'll have to do longer distances to visit Istanbul. This was perfect for our needs, though :)
Eyüp was very nice, always accomodating, checking in from time to time on Whtsapp to see if everything was alright, which we appreciated!
Explore a little bit yourself without always relying on GMaps, because the area seems very new, so not all shortcuts and stairs are showed on the map, but they're easy to find :)
Finally, little reminder that Istanbul goes up and down a lot, and this apartment is more up hill, so be prepared for some good amount of stairs when coming back to the place :p But it's alright, you'll have lots and lots of kitties everywhere to keep you company during your walks!