I loved staying at Callejon Dolores 8 in El Centro Historico/Barrio Chino!
The room is lovely. Irina provides everything including cleaning supplies, an emergency kit, extra sheets and blankets, and even umbrellas. The only issue I had is that the room can get hot and when you leave the balcony door open mosquitos fly in. But once I bought a mosquito repellent (only $4usd) it wasn't an issue anymore. The shower is also amazing. Sometimes the hot water will run out but if you turn it off for a couple minutes it will come back on.
The apartment building is very beautiful as well, it has an elevator, laundry room, common space, and gym which makes it convenient for extended stays. The location is literally in the middle of barrio chino and is close to several metro stops, historical sites, shopping and restaurants. I personally preferred this neighborhood over areas like Polanco and Zona Rosa where there are more ex-pats, but some might feel it's not as nice. The wifi throughout the building was strong enough to have video calls in my apartment and in the common space. The best part of the apartment is the attendants. Jaime, Cesar, and Samuel are incredibly friendly and helpful!