The movie The Messenger: The Story of Joan of Arc(1999) is pretty good with the stuff of the 15th century if you need inspiration. As I recall they show soldiers in various stages of dress. There is a garment call a pourpoint (or arming jacket, or gambeson) between the regular clothing underneath and the armor. I can be worn by itself or armor can be tied onto it with points. There is a cool one called Pourpoint of Charles de Blois. (I'd post a link but I'm new enough that my posts with links get lost.)
Did you want to do Joan's era or would anything medieval do? My background is in historical reenactment so I can go from excruciating accurate to just getting by.