I left my accommodation booking to the last minute and had a lot of trouble finding a place, but eventually I found Felipe's flat. He was very quick to reply to messages. It is very good value, about 10 minutes walk from Embajadores metro station and the neighbourhood is nice. You can walk to most tourist sites in 15-30 minutes.
The other people who I met in the flat were friendly, generous and helpful.
I was able to practise my Spanish with Felipe and his flatmate, and his brother speaks good English.
Next time in Madrid I know where to stay!