Place a chest of drawers, doubling up as a study table, made of oak and branded with iron instead of the regular cupboard. Upholster the chair in heavy brocades in medieval style. A castle bed with bronze leaf finish would complete the effect.
Having a heavy tapestry with ancient designs or flowers on a window with stained glass can keep out the draft and will also impart a grandeur to the room. They can also be hung around the bed to maintain the privacy.
Tall candleholders made of wrought iron and rugs with ancient Gothic designs will impart a castle feel to the room, as will decorating the walls with a helmet, sword and shield. Placing a knight's statue with brass armour near the doorway will add to the statement of the room, giving it a Gothic feel.
A medieval room is incomplete without oak beams on the ceiling, which also give a warm finishing touch.