I'm trying to get a sense of some of the style and logic of popular "commonsensical" or everyday parables/legends/sayings that would've been widely known in Italy during the late medieval to late Renaissance period, along the lines of the story of St.Augustine and the seashell- any help on good sources or places to look would be greatly appreciated!
The Golden Legend was one of the most widely read texts in the Late Middle Ages. It was written by the Genoese Bishop Jacopo da Varagine and gathers togethers many of the saints lives circulating at the time. I would, however, caution you against referring to something like this as "Renaissance." The term Renaissance brings to mind a specific type of humanistic "high culture" rather than a time period. I think "late medieval Italy" might be a more apt descriptor of what you're looking for. Just something to consider.