I spend a week with a friend in Barbara Leao's apartment in Alfama, in July. It is a very nice place, with a beautiful view on the river and the neighborhood is lovely, with lots of little streets, it is called the "heart" of Lisbon. It is close to the bus, tram and metro (5mins walk) so it is practical. The host, Barbara Leao is very kind.
I highly recommend this place if you want to visit Lisbon with a friend or as a couple!