What a great place to stay.
The location is perfect in the city center, right next to Campo de'Fiori. Most major sights are in walking distance and if the walk seems too long, you can take advantage of many public transport options nearby. Campo de'Fiori itself has many restaurants and cafés. During night time it's popular for its bars, but the windows didn't let the noise into the apartment, so you'll be fine.
The apartment itself is beautiful. We really loved it. It's located in a historical building where a pope's mistress used to run an inn centuries ago. It was spotless clean, newly furbished with lovely touches. The best thing was the super comfy bed though (which I think is most important when staying away from home). The apartment is air conditioned which I found to be very convenient in the summer heat (and I'm from Europe and used to not having A/C everywhere I go, but for American visitors this information might be essential).
Polly is a very lovely and hospitable host. We felt instantly welcome, she was very responsive to questions and offered to help us where she could.
We would definitely come back.