If you have limited sewing experience, you can simply throw an overlarge piece of medieval looking material over your saddleblanket; something that will go from withers to tail and halfway down the sides leaving the front open. You will be able to canter and jump in this.
Next, take some of the same material and make a long sleeve or tube to slide over each rein from bit to where your hands will go. If you have time to sew fringe on the bottom of the reins and blanket, it will show it off more.
Cover your breastplate the same way and it will match.
Make some tassles and attach them in various places where the bridle leather makes a cross, at the bottom of the bit, even some shorter ones across the browband.
Braid your horse's mane in that one, continuous braid all along his neck, weaving a matching colored fabric into it, but something that contrasts with the mane.
Take pictures and let us see what you come up with!