Want to rent a room in the centre of Madrid

I am a 21 year old student and I am coming to madrid on the 15th September to work for 7 months. I would like to rent a room in a nice modern apartment preferably with a double bed near the centre of madrid. 

I don't smoke, and don't have any pets, and am very clean and easy to live with. I would ideally also like to live with people who are spanish since I am coming to Madrid to improve my spanish.