Search through some of these for ideas: https://www.hometalk.com/search/posts?filter=diy%20headboard
Here are some more ideas: https://www.architecturaldigest.com/story/easy-diy-headboards
try this: https://www.craftylittlegnome.com/diy-upholstered-headboard/
Have you seen this one? https://www.hometalk.com/20179113/make-a-diy-headboard-out-of-plywood-
I put thin strips of wood on the wall in the oblong shape of a headboard, painted the wood then used stencil and paint within the frame. IT is stunning. Now friends want me to do one for them.