Or you the "Voi" (You all) form.
So for example while talking to one person to ask where he goes on vacation, you say: "Dove andate Voi in vacanza?" (Where to you all go on vacation? even though it's only one person you are talking to).
The formal "Voi" form (and the informal "Tu" form) was the only formal way in Italian during the Middle Ages and the Renaissance.
The "Lei" form, with the use of the 3rd person in the singular, was adopted in the XVI/XVII century, probably due to the influence of Spanish culture in Italy (most of Italy was ruled by Spain then), since the Spaniards use the formal "Usted" which requires the use of the 3rd person singular.
So both the "Voi" (originally Italian) and the "Lei" form would be acceptable formal forms. The "Voi" form became actually mandatory during the Fascist regime, because Mussolini considered the "Lei" form not authentically Italian (had in fact a Spanish origin) and also he considered the "Lei" form effeminate and not manly enough (he believed in virility).
The "Voi" form has however fallen in disuse and is still (rarely) used with older people (especially those who grew up in the fascist era, most of whom have now passed) and maybe in the South. I remember when I was young, that people of my grandparents' generation were using almost exclusively the "Voi" form.