When it comes to Renaissance costuming, one piece that almost immediately comes to mind is the Giornea. This dress was the top most layer worn over a house dress and a chemise. It is often sold at fairs and festivals as a starter piece for the women’s wardrobe. The first medievalish costume I ever bought was one of these dresses.
An excellent artist to look at when considering your overdress is Dominic Giorlandio.
This is a simple tabbard like garment. Open at the sides, it is worn belted or loose.
Dressing Renaissance Florence: Families, Fortunes, and Fine Clothing. Carole Collier Frick, The Johns Hopkins University Studies in Historical and Political Science, 2002.
Dress of the Venetians. Stella Mary Newton. Scholar Press, 1988.