I have no idea how I just stumbled upon this medieval guide to underwear (and other clothing) - in Polish: http://goncza.pl/baza-wiedzy/stroje-meskie/stroj-meski-bielizna

It's definitely worth looking through, though, as it has lots of period images, often with isolated close-ups, much in the style in the Company of St George men's clothing guide. For example, here's the collection of braies:

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And here is just one of their collections of examples of hosen:

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Enjoy!