Casa Cosi was perfect! It is a beautiful apartment located in a great area that is fairly quiet but at the same time super convenient and close to major sites and metro stops. The apartment itself is large and although we were only 2 people, could certainly fit more if necessary. The smaller room, however, does not have an AC inside of it so could potentially get hot with the door closed.
Otherwise, everything was incredible about the apartment. And it's right next door to a charming cafe Can Joan where we ended up getting cafe solo every morning. It's the little neighborhood touches that really make this place.