I found this great project on Crafts n’ Coffee; you can read the details, along with instructions, here.
First, I used the template provided on the website and enlarged it to be the appropriate scale for behind my couch. Next, I chose the different yet coordinated fabrics (way more time-consuming than expected!), followed by cutting the Styrofoam and putting it all together with a lot of ModPodge and Gorilla Glue. Here are some photos of the process.