I highly recommend staying with Antonella! Her flat is super centrally located--it's accessible by the Metro (~10 minute walk to the Spagna station) and within walking distance to all the major sites in Rome. The space was sufficient for me and my sister, and the bed is definitely big enough for 2 people (and really comfortable). Just make sure you're able to walk up a couple flights of narrow stairs with your bags.
In addition, Antonella is the perfect host--she's super friendly and welcoming and I immediately felt like I was at a home away from home when we met. Communication was clear and open throughout our entire trip. The check-in and check-out process was really streamlined, and Antonella provided really helpful restaurant and activity recommendations for us. If you're considering this listing for your trip to Rome, definitely book it while it's available!