Reddit mentions of Medieval Garments Reconstructed: Norse Clothing Patterns

Generalizing grossly, for undergarments, you'll want undyed linen woven plain. For top garments, you'll want wool either natural sheep colors or dyed with madder or woad and woven in a twill pattern. Wool yarns should be worsted spun and 2-ply (I think? I want to say 3-ply happens, but isn't as common). I don't have setts in my head anymore, but they're finer than is typically used for modern weaving.

Twill patterns depend on what period you're in, to my recollection.

There are also a ton of different kinds of narrow wares (ribbons, lacing, belts, garters, etc.) which are woven using a variety of different methods, but that is an entirely different barrel of monkeys.

OK, references!

Textile Production at 16-22 Coppergate (goes to a PDF; focuses mostly on 9th-14th/15th centuries) -- Definitely, definitely read this one. It's free and covers textile production from beginning to end.

Textiles and Clothing: c.1150-c1450, vol. 4 of Medieval Finds from Excavations in London

I also want to suggest Woven into the Earth and its partner book Medieval Garments Reconstructed, which are about the medieval finds in Herjolfnes, Greenland. However, the settlement in Greenland was cut off from the rest of Europe for a long time, so the finds don't really represent what was happening on the mainland at the time. You might find the weaving patterns useful, though. Possibly the clothing patterns?

ETA: There was also a recent discovery at a castle in Austria of a bunch of linen fragments of undergarments. Beatrix Nutz is the main researcher, but I'm not sure if she's published her findings yet. I lost track of the research. Here's a blog post about it with some thread counts for the linen.

It wasn't the ONLY issue, but the most frustrating one. The pieces for the arm and gores in that area didn't fit together right at all. I ended up having to redraft to make a proper fit. That was just an mild annoyance though compared to the devastation of loosing the fabric from the length issue. Of course, it wasn't devastating for me because I had another use for the wool but for somebody else it would be awful!

If you're interested in the Greenland gowns, I'm sure you already know, but if not I feel the need to point you in the direction of this and this. I haven't actually tried to use any of the patterns given in the second book but the research and photos are simply astounding.

I know by this point most people interested in the topic have heard of and seen these books but they are so interesting I always have to point them out just in case somebody hasn't seen them yet and I can blow their minds the way that lady from Smoke and Fire did for me when she showed me these books.