Padded cuisses with steel knee cops - 13th/14th century base garment for wearing/attaching armor. For sizing, I recommend you go with whatever size you would buy in sweat pants. The cuisses are also relatively custom-fittable - they have adjustable laces up the back. Made by Get Dressed For Battle (GDFB).

Sizes available:
L (26"-29" circumference, 22 1/4" length)
XL (27"-30" circumference, 22 1/4" length)
XXL (28"-31" circumference, 22 1/4" length)

Discontinued and sold out