Wow - this was a really wonderful experience, much better than I would have anticipated. Macarena and her son were both so warm and accommodating. The room and private bathroom next door were simple and provided everything I needed for my stay in Madrid, including a nice workspace with FAST internet and plenty of privacy. Macarena gave me the keys to the building and the apartment with a quick explanation and, from there, I had the freedom to come and go as I pleased. Her son is fluent in English (as well as at least a couple other languages) and was so nice and helpful with suggesting places to check out in Madrid that I wouldn't have known about otherwise.
Beyond being excellent hosts, Macarena and her son are genuinely nice and interesting people and I would honestly consider them to be friends after a stay of just one week. I sincerely hope that I can return to Madrid soon and this will be my first choice for a place to stay, presuming it's available (I imagine it's popular!).
All in all, a great experience and a great deal - excellent value for the price. Highly recommended!