We can highly recommend Carla's appartment! It is located in a rather quiet but still convenient neighborhood with nice parks very close and a stop of Tram # 28 only two minutes away. Bairro Alto is around the corner and the city center is also in walking distance.
The appartment itself, despite being slightly dark, is furnished with a love for details and is so well equipped that you instantly feel at home. Plus Carla is a perfect host: very supportive, extremely friendly and really wanting you to have a perfect stay! If we ever come back to Lisbon, we'll make sure to stop there again!