Go for a drive in the name of safety to a dealership and try on everything there.
I had no idea what size or shape my head was, so I literally tried on every style, shape, color, make, and model helmet on the display shelves. Then I left and got a better deal online. Good thing they didn't remember me after that trip since it was my first time ever in there.
now they recognize me by my bike and I stop in periodically to gawk at new gear and bikes. what a winner I am