I would highly recommend staying at Sinem’s Apartment to anyone. Kartal is a wonderful and tranquil neighborhood on the Asian side of the city where you can return refreshed and sleep well. You will also be surrounded by some kind local Turkish neighbors and may easily have a pleasant dining experience at the neighborhood eateries.
In terms of transportation, there are numerous bus stops that are "a walking distance" from the apartment where you can take one to the Marmaray and then take another to anywhere you need to go.
We appreciate you hosting us Sinem, and when we return to Turkey, we will definitely reserve the same flat.