We had a lovely stay in Lisbon thanks to Joana and Diogo's well located flat. The neighbourhood, bairro alto, is one of the most lively of the city and can be very noisy until very late at night. The bedroom being in the back, we didn't hear much and slept very well nonetheless.
The flat itself was great: lots of windows so it was always fresh, with a fully equiped kitchen. The bed was very comfortable. The bathroom was small, but not claustrophobically tiny (loved the shower!).
Few tiny warnings: the flat is the uppermost one of the building and the stairs are high and narrows. Joana and Diogo own the whole building so if you have issues about climbing stairs, maybe look for the other flats of the building because they are great tenants.
Also, about getting there, the nearest metro station is Restauradores. If you carry heavy luggage like we were, do not trust GoogleMaps to get you there! You will climb a very, very steep alley, called calçada da Gloria. Unless you take the funicular on that street, you will have a very bad moment.
But hey, the hills are a great part of Lisbon's charms! And even with those little "issues", we strongly recommend the flat for a wonderful and authentic experience of Lisbon.