Fit is very important; even within the same size, different brands fit me very differently as noted above, some would have been very uncomfortable. I didn't have any shops nearby to try different helmets, but Northstar Motorsports was great about sending me several helmets to try, then return the ones that did not fit. I don't recall if I had to pay for all of them initially and get a refund on the returns, but I don't think so. Probably other places would do the same, but Northstar were great do deal with.
https://www.northstarmotorsports.com/