For sewing the pillows, I needed to find a good place for a seam - in the end I figured out that if I continued the black fabric all the way over the lower layer of foam, I could fix it with velcro to the base gray fabric and also use velcro to fixate the fabric for the two pointy ears of the pillow. At the very end I decided to sew corners into the black fabric as well, so it would be really tight around the lower layer foam, and stay tight.

In this way, the pillows can still be opened up to fix possible issues with the wiring inside, or for transport, as it turned out when I had to pack the suitcase.