I can only reinforce what so many others have said about Cristiana's place. It's as central as you can possibly get in Rome. The terrace is a wonderful bonus. Cristiana was an excellent communicator and really acted as a true "host" for my time in the city. She even arranged a car for me from the airport due to a national transit strike, even though I wasn't due to stay with her for almost two weeks! Highly recommend and would certainly stay again on my next trip to Rome.