I spent a really amazing amount of time cocking around trying to find a pattern for the semifitted Burgundian gown that followed the houppelande, so in case it helps anyone else, here it is.
Go. Note that you will need a muslin (here called a "block") and a basic idea of how patterns work. It may not be totally period, but I've tried both and my days of cocking about with simple rectangles and hoping to fit it on the body through basting and faerieskilz are totally over.
Make a muslin. I thank the textile gods every time I go down this hole, that I have a mom who can sew and was brought up in days when Home Economics meant "you might have to earn a living doing this", so can French seams and read a pattern and adapt measurements for when you have the chest and shoulders of a preteen boy and the lower body of a Clydesdale.
And a dear friend who majored in this sort of thing, who took us all pattern shopping and measured us and helped develop the base pattern that formed the muslin for the bridesmaid dress I still get compliments on to this day <3