I bought one of those horseshoe shaped pillows that you take on planes and I wore it the other day when I was in the passenger seat and leaned my head against the headrest and it was great cushioning and kept my neck braced.
I haven't tried it as the driver yet. My doctor wanted to give me a neck brace today but they didn't have the right size. She said i shouldn't be wearing it when driving as it could impede head movement when needed.