My stay at Marzia's place was just lovely - the room is completely separate, with its own entrance, though if you need anything at all Marzia is just on the other side of the door!
The location was great for the Vatican (literally a 5 minute walk), and about 15 minutes from Piazza Navona.
Oh and if you are planning on taking a cab from the airport, ask Marzia to arrange a driver - you pay a flat rate in a cab anyway and for the same price you can travel in style... A very glamorous way to arrive in the Eternal City!
Breakfast is a coffee and cornetto at the cafe downstairs - a few doors the other way is an excellent pizzeria called Goose (!) It's well worth checking out if you've need a break from the madness of the city centre!