Before leaving your village to Venice, go to the upper exit of the village and go to the left to an open area with quite a few assassin's. Defeat their leader and you will get the item Leather Mail (unfitting). If you have already 500 ducats, you can ask Mattheo to customize the armor for you. If you do not have so much money yet, sell all the swords, go and collect copper ores to sell, etc... or simply wait until you have the Smithy in Venice and let Mattheo customize it for you then.