I would like to stay at a convent in Rome but my first choice is booked up, Suore di Santa Elisabetta. The one by the Vatican is available but I wasn't sure if that would put me too far away from everything else. I wanted to be able to walk to a few key sites like the piazzas, pantheon or forum. I also wouldn't be a opposed to a reasonable priced bed and breakfast.
Have you checked out santasusanna.org, which is the american parish in Rome? You click on"coming to Rome." and it will give you a list of convents to check out. We usually stay at Santa Maria alle Fornachi, which is near the San Pietro station and about 5 minutes from the Vatican, and (for us) is within 25+ minutes to most of the attractions. You can use Google maps to see if this would work for you. Also, they will schedule a cab for you at 6am to get you to T5 for your flight.
Yes, Santa Maria alle Fornachi is the one that responded to us that they have vacancies. I think I liked the price more than anything else. Are there pretty views from this side of Rome? Are there many attractive common areas in the convent to eat breakfast?
Last summer I stayed at Santa Anna, near the Colosseum, and although breakfast was quite basic (instant coffee and a huge roll), I had a great time due to its location. It's on a small piazza, so ask for a room at the back if you crave quiet. I paid about 50 euro for a single with bath.
Santa maria is pretty basic(check TripAdvisor.com) however, it does have a very nice breakfast and superb coffee and service.