If you'd like, these are the schematics I fashioned to make mine, as well as a photo of the finished product. You're free to use them as you see fit.
As noted, the "shell" of it is made of two end-caps with a large piece of fabric between them. On the seams, sew on a strip of black fabric or ribbon as a border.
When finished, shape the padding by cutting sheet foam in your ideal shape of the pad to fill out the pillow how you'd like.
When done, it should look a little something like this:
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Looks like you are doing a really good job so far!
Seconded, sounds interesting!