@Antaeus Yeah it is a bit limited if you want to stay within solely the Norman look and go no further than 1100.
However there is some potential still. A mail coif is a good idea. Speaking of mail, a nice neat-looking mail shoulders item could go well. And a large cloak would be nice.
You could also take inspiration from earlier Western Europeans than the Normans. Maybe some "crenellated" looking cloth belts and fringes, as in 3 and 8.
Seems like just a couple more shoulder pieces, and perhaps a singular new torso piece and head piece, is all that's needed to round out the Vlandian aesthetic.
Another easy way to add visual diversity would be to apply faction-coloured paint to existing helmet pieces, as one guy did in the Creative Unit Aesthetics Archive. And you could add a golden belt to existing tabards to make a "luxury tabard".
Thanks for the input, which slot would you say is missing armor variety for low tier troops? Head, shoulders, torso, lower legs/feet, lower arms/hands?