Pablo's flat on Plaza de Tirso de Molina is superb. It's situated right on a lively plaza, with a busy restaurant/bar on the ground floor, yet the bedroom is virtually silent. We stayed in January, which was pretty chilly, so the windows were closed. The bedroom and living room each have two heaters, so it was quite warm and cozy despite the cold weather.
Other pros: very clean; abundant hot water in both the bathroom and kitchen; great views from bedroom and living room windows; small but sturdy elevator (ten stairs from the building entrance to the elevator); 1/2 block to the beautiful Tirso Metro station; very short walks to fine bakeries, fresh produce shops, restaurants, and even a 24 hour supermarket.
One con: for us, the foam mattress was a little too soft.
Things to note: the roof beams get a bit low in some places--could be challenging to someone over 6'; the only coffee makers are two stovetop espresso makers (which we had no problem with); pantry basics are erratic, e.g., some teas, but no coffee, and olive oil, but no vinegar. However, there was plenty of toilet paper and towels, napkins, etc..
We'd happily stay there again.