I can’t tell you for Traviata in 2019, but I got there 2.5 in advance decades ago to grab balcony tix for second balcony center for a ballet because it’s an Italian-style theater, in which only those few directly across from the stage have the honor of seeing the whole stage, while everyone else in the theater can see these persons of standing.
Far from this anointed box, I did sit behind a pole in the stifling top balcony, known as paradise, close to the Chagall ceiling back when I was young and broke for La Bohème. My husband and MIL didn’t have a pole, so they saw the top of the wigs.
Since La Traviata is completely sold out, I’d Be there VERY early. Paris has a lot of broke opera aficionados. Or, Madame Butterfly at the Bastille has tickets available. Even in the less expensive seats, you’d be able to see, with binoculars, and the acoustics are excellent. Then you can take a tour of the Garnier.