I can't recommend this place enough. The best place we stayed on our 8 day trip to Italy.
This is an inexpensive little place with a cool vibe, right in Campo De Fiori. Like others have said, it's a few flights of stairs up, but we didn't mind. There were some birds on the roof that were pretty loud, but maybe that only happens around late January. One thing we noticed was the beds in Italy don't seem to be as soft as what we're used to in the US, but after a long day exploring, we were too tired to really notice.
Federico was very responsive and helpful. He left a book of information and tips for us. I recommend Fatamorgana, the gelato place down the street, and Roscioli (their bread basket will change your life) and Barnum Cafe, two nearby restaurants. Another plus: this place is only a 5-10 min walk form Piazza Navona and the Pantheon. And since this place has a little kitchen/coffee maker/fridge, you can come home and make yourself a meal with ingredients you bought at the market in the adjacent square.