I just found a reference to a fairly recent archaeological find in Lengberg Castle in Austria, which included a whole bunch of textiles. Have a look at this link, in which it is mentioned that amongst the finds are several "nearly complete linen bras", and one that even has quite a modern look despite most likely having been made already in the 15th century! Now I have been searching for pictures of these bras but I can't find any. If you have any links or other info, please share them with me! I am incredibly curious!
Another interesting link, which I got from a stitch in time, shows a few pictures which are pretty interesting. Check out the panties, also from Lengberg Castle! Perhaps it is actually time to do some medieval underwear, instead of cheating like I have done so far?