If you don't mind staying a hair off the beaten path, Marco's place is perfect.
We walked and/or took the metro for all our travels and his home is about a block from the San Giovanni metro station and a 20 minute walk to the Colosseum (which is due west). The apartment has everything you can think of and Marco is quite the Renaissance man so you'll find all kinds of interesting things inside that surprise you. Kitchen and bathroom set up for all the primary things you need, and since we too were backpacking we only brought 4 days of clothes and used the washer and dryer. Very comfortable bed (which we so appreciate) and really the whole place is cozy. Just a great jumping off point for everything we did in Rome. We plan on making this our home base again on our next Italy trip!