More a 3 star than 5 star, but for what its worth...

My fairly picky mother, who doesnt walk well, has stayed in Albergi Caesari on two separate trips to Rome, once both before and after a cruise. She liked it. Not sure if there is a true 5 star that close to Navona, so you may have to balance proximity and stars. Mom was able to walk there easily, so any able bodied person can grab a tartuffo with minimal effort. Probably 4 stars in the US, but ratings are strict.