Also used in Portuguese. It's definitely more common for the older generations, but I've known a few Perpetuas (my dad has a cousin whose wife has this name). We spell it Perpétua. I actually like it, but it probably won't work unless you're really religious. [noted -ed]
This is a quote from the user Murasaki on the Name Facts board on the usage of the name Perpetua in Italy. "[Perpetua] has a history of usage in Italy, and has been used in Alessandro Manzoni's 19th c. classic novel "The Betrothed" where it's the name of the character of a priest's governess. As a result, "Perpetua" has become a common word to designate a priest's governess, and has consequently fallen out of use as a person's name."