my Templar persona is late 12th early 13th century. Mail is indeed your friend.
For my kit, which to fight in the Adrian Empire requires more stringent armour than period, will have hidden knees, cuisses and greaves. Basically I'm making my legs very similar to 14th century in that the greaves, cuisses and knees are all attached, but the splints are hidden underneath a layer of canvas that's channled to appear to be gamboised. The "hinge" is my low profile DonJoy knee braces. Over that goes my mail chausses. My hope is that it looks as good as I can get it to period with the extra armour. Worst case scenario, my sleeveless surcoat or habit.cappae will help to hide it all.