Under the armour, they wore a simple tunic with pants and then a mail shirt. All the clothes were made of simple fabric, not fur because it would make them sweat a lot and they needed the armour to be close to their bodies to be more comfortable. You can search for images of movies of Joan of Arc for getting inspired.
Working on: Astrid (HTTYD) Toothiana modern human versión (ROTG) Secret cosplay
Future cosplays: Astrid's Heather costume (ROB)Anna (Frozen)