I have a TON of feathers that we can put in your horses mane and tail for that costume. I also have a lynx pelt you can wrap up in OR a soft mount fox that you could drape across your lap. It would go with the Bo, like you just came back from hunting.
We could put feathers in your hair as well. I don't have any buckskin dresses or else I would offer one to use.
I also know how to make a war bridle, but it's not for everyday use as it puts a lot of pressure on the horses mouth. I think a costume would be alright though.