The communication with Maria and João was very easy, they always responded quickly to any questions we had (we used SMS mostly), and made sure we had what we needed and knew how to get from/to the airport. They also recommended a great fado place and even booked it for us, and it was an amazing experience! Really good quality fado and good food as well (4 courses). Thanks!
The apartment itself has the best location you can get, I think. Just a couple of streets away from Bairro Alto and one hill down to Rossio/Baixa. Smack in the middle of everything, but still a very quiet street - a rare thing in the center of Lisbon. Also, it is next to a lovely square with restaurants and the ruin of Convento do Carmo, plus there's a great restaurant on the corner - Faca & Garfo, which I recommend. It is a very old apartment so the finishes aren't exactly perfect, but it has a lot of charm, cute decor, and it was nice and clean when we came - which I think is most important. It is not very insulated, so I don't know how warm it will be in winter, but at least there are proper duvet covers there. Beds were firm and we all slept well. It is also a practical place if you are several people, as there are 4 separate bedrooms in addition to the living room. Sufficient hot water for us (we were 3 people) and a fully equipped kitchen. I was a bit worried about the stairs up to the apartment, as I was travelling with my parents who are 70 years old, but it proved no problem at all - 2 stairs up that are easy to climb, and in addition João helped us with the luggage when we arrived. All in all, a perfect base for exploring Lisbon, Maria and João are excellent hosts, and my parents were happy I talked them into trying AirBnB instead of a hotel:)