Go to a flea market and look for decorative doors. Some are beautiful. Then paint or stain to your liking. I've even used a picket fence, painted it, and painted flowers on it.
Here are several ideas https://www.hometalk.com/search/posts?filter=headboard
here are some ideas: https://www.hometalk.com/search/posts?filter=double%20bed%20headboard
Maura, there are many ideas in hometalk DIY, I have chosen a few for you: