My 10-year-old son brought home a book from our park’s free library box. It was a biology textbook – teachers edition. He said it looked interesting and hey, it was free (having no idea you could sell it). I scanned it in my Amazon seller app and realized it was worth around $150. He was so excited. We listed it for sale for $130 and it sold! Going to tell him, he just made $130!
People are turning to audio and visuals when it comes to technical subjects. However, you should consider doing an ebook first and turning it into an audiobook through a resource like Audible's ACX platform. You can hire a producer either through a royalty share program, so you don't have to shell out upfront cash, or you can do a pay-per-hour hire as well.
I recognize that the list above is short; however, that’s because Amazon affiliate marketing really doesn’t require a specialized theme in order for it to work well (unless it’s one of the unique cases noted in the themes above). Instead, you’re better off using WooCommerce if you want to build a full affiliate store or simply stick to the WordPress theme you currently have and add affiliate plugins to the mix.