When Dave and I bought this house about two and a half years ago, we were surprised when our bed didn't fit into our 3rd floor bedroom. Being new homeowners and thusly, broke as all get out, I went to Ikea and purchased the cheapest bed I could find, thinking that we could take the boxes up the stairs and put the bed together. We really wanted a nice, upholstered headboard, but everything we liked was at least several hundred dollars. Here's how we got exactly what we wanted for about $150.
Dave sawed off the tips of wood that jut out at the top of the frame so we'd have a neat, rectangular shape to start with. Then he took a piece of plain ol' fiberboard and cut it the same size as the headboard so I'd have something to upholster over. A mist of spray-mount holds the foam in place.