Jaime's place is great in all aspects, I highly recommend and I would definitely return.
The room was clean and had a kettle and a fridge and a coffeemaker (but I didn't use it). It's close to all the main locations, and is itself centrally located. Carrefour that's open 24/7 is very near the place, which makes is convenient.
The Wi-Fi, the shower, everything worked great. There's a fan in the room, which made the room comfortable temperature even though I stayed in the middle of July when Madrid is hot. There's plenty of sunlight, too.
I think it's ideal for a solo traveler.
Also, Jaime was flexible about my travel dates: he accepted my request on the day of my arrival, and was understanding about my uncertainty in terms of when I was leaving. The check-in process was also great with clear instructions.