We had a great stay at Elsa & Gabi's apartment. It is small but very well planned out and has everything you need. Fantastic information pack sent over to us giving recommendations about where to visit, where's to eat, drink and other 'must do's'. The bed was firm but comfortable although we would have liked an additional pillow. The only minor issue was that you could hear the drainage when the apartments above where using the bathroom which did wake us on occasion.
Overall a great stay and we would stay again when visiting Madrid!