I use an old pillow case and fill 3/4 full of scraps. Sew the end shut. Then sew in channels if you want to. My 10 pond dog loves to rearrange the pillow before laying on it, so I don't put in channels.
If I give one away, I put another pillow case on it or make a cover out of old bath towels.
When i need a bigger pillow i use old bed sheets and cut to size. All the animals love them.
I can put everything in the washer and dryer.