Crucial in this conversion, I think, is having access to some woodworking equipment. A few years ago, I got into woodworking with a basic setup that included a jointer and planer. You need these to size the wood to the correct size.
The main component of the bed is a 1¼”x1¼” wood frame. As a type of wood I chose hickory, only because I had enough of it laying around; poplar would be a good choice too, just keep it as cheap as possible. Unfortunately mine was 1″ stock and that is before jointing and planing. So over the last few weeks I have been gluing boards together, sawed them to rough widths and finally jointed and planed them.
Then I started to pre-assemble them in my garage/workshop. So far looking very small and flimsy, but assuming that will change once installed.