What gopro accessory should I buy that would be best to film a roller coaster POV?

I want to film a POV video of me riding a roller coaster with my gopro. The roller coaster does not go upside-down, but it goes up to 50mph. What gopro accessory would be the best for this? A chest harness? A gopro helmet with a headstrap? Or something else? Thanks for taking the time to help out!

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