If you haven't already discovered this, and you're handy with a staple gun and a drill, then here's the simplest way to create custom upholstered headboards for your inventory 'without re-inventing the wheel!' I've used it so many times, I can't tell you. Enjoy.
click this link to Martha Stewart's website...(Yes...I know...MT!): Upholstered Headboard Craft
NOTE: Just have your local dealer pre-cut the hollow door for you before leaving the store. Home Depot, Lowes, and most of the "big box" home improvement stores provide cutting services. Sure beats doing it at home, and the door fits easily inside your vehicle (assuming you have a vehicle that can accommodate). Cheers.
Another site to find templates and ideas: http://runninglawyer.blogspot.com/2011/08/diy-upholstered-headboard.html