I did see people carrying their pillows, but on spirit there really isn't enough room. So I just took a lil pillow that wrapped around my neck and it was perfect size.
Most airlines allow a pillow as part of your personal items, just make sure it can fit (or attach to) your bag
Look for a turtle.. its really great . Over all I don't think there is a size (I've seen kids with full sized pillows). There are great head/ neck pillows as well.
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