Leather pauldrons, also known and shoulder armor, available in the medieval style. One size fits most.
These were perfect for my cosplay. I was wearing them over a cloak, so I bought a few 12.5mm fasteners to use with the two that are on the pauldrons. They stayed in place securely and held their shape. I am 5'4", about 140 and there was a strap setting that fit me well. I trimmed the excess.