>>14744812the ulthbert stuff is ok - for larping, certainly good enough
you might need to look at adjusting the strapping inside, I sort of recall that they have a spider inside for fitting and adjustment. it makes sense to sew up a padded coif too, to go under it, particularly if its a wee bit loose. I'll try to dig out a pattern before the image limit's hit...
something like this one, though. you can make it from about a foot wide section of cotton or linen, and pad it with towelling or the likes, sort of like a quilt.
they'll take the knocks and help it fit more comfortably.
not hard to make at alll..