Martha's place is by far the best option I could think of if you want to wonder around this part of the city (the south). It's pretty close to the Centro de Coyoacan, and to the museums, mercados, and plazas around this area. Both of her apartment are spacious and with a good and peaceful vibe despite the vibrant ambiance of Coyoacan outside. I'd definitely stay here again and recommend Martha as your host, she is very kind and stays in touch for everything you could need.