However, one set of resources that I do trust is the series of books published by Boydell Press and the Museum of London. These volumes do a great job of presenting information based on actual archaeological finds in a friendly visual way that everyone can understand. You may remember The Medieval Horse and its Equipment, which I mentioned some weeks ago. It's part of that series as well.
Here are the other titles.
Textiles and Clothing, c. 1150-c. 1450 by Elisabeth Crowfoot, Frances Pritchard and Kay Staniland
Shoes and Pattens by Francis Grew and Margrethe de Neergaard
Dress Accessories, c. 1150-c. 1450 by Geoff Egan and Frances Pritchard
Knives and Scabbards by Jane Cowgill, Margrethe de Neergaard and Nick Griffiths
The first two links lead to Google books with a limited number of pages and the last two give you only snippet views.
I can also think of a couple of books that don't belong to the series but present the same sort of information in much the same format.
Fashion in the Age of the Black Prince: A Study of the Years 1340-1365 by Stella Mary Newton
Purses in Pieces: Archaeological Finds of Late Medieval and 16th-Century Leather Purses, Pouches, Bags and Cases in the Netherlands by Olaf Goubitz. You can download the first thirty pages of this book from the publisher's website.
These books would be the first place I would go if I were thinking of making an accurate medieval costume.
Fresco at Runkelstein castle at Bolzano, late fourteenth century.