Compared to a lot of games and other fictions set in or inspired by Medieval Europe often we see plate armor being the 'heavy' choice especially for professional fighters, than maybe leather or chain mail for militias or more mobile fighters. Is that mainly what would be on offer if you walked into a real medieval armor shop?
Did you have a period and region that you have in mind? Armour changes a great deal through the Middle Ages and is somewhat dependent upon region as well.