This was an old pillow case I'd had for years. Having been in the military I've got tons of these brown t-shirts lying around. Since that was a loooong time ago they don't fit me anymore. Upcycling seems to be my new favorite thing. I have tons of clothes that were going away to goodwill. They Will be Good once they are made into something new.
Here's a close up of the back. I used some circular elastic and a button I found
Side Note: I now understand the need for interfacing.
Knit doesn't seem to keep it's shape, especially at the collar.