A regular bucket hat would do, a lot of archers wear them, I’ve got one and it’s just right, enough brim to shade my eyes and the back of my neck, and the brim is pretty stiff and doesn’t flap around. I usually go along to the club on Saturday morning, when the sun is already fairly high, and Tuesday and Thursday evening, when the sun is shining directly into my eyes, the brim is exactly the right width to shade my eyes and I can still see the target.
I’ve also got an Australian military camo one, they call them giggle hats, the reason why completely escapes me, it’s got a slightly wider brim but it’s a softer material and it will flap around a bit in the wind – I reckon a bucket hat would be your best bet.