Carlos apartment offers the best possible base for a stay in Lisbon. It is extremely well located, right next to the train station (<30 minutes from the airport) and metro station. The city centre is <20 minutes by foot and already right next to it are great shops and restaurants (e.g. Restaurant Maçã Verde, a great authentic fish restaurant with very good value for money, or Arcaz Velho, a place where we had a fantastic dinner with Fado life performance).
Carlos himself is a super nice host who replied immediately to all my emails and really made our stay something special.
I definitely recommend staying at his place!