Take a Look mirror

[cosc]

I also found vibration much less on my sunglasses than helmet.
I would go with the larger mirror.
I've seen some mirrors adjusted with the lengthwise vertical, but I've always had mine lengthwise horizontal. Someday I might try it the other way but I've been satisfied. I think mirrors can be a lifesaver especially since I ride on a road with lots of traffic. I do like to know when I'm king of the road or not.
Women here have given you great advice, just give your brain a chance to adapt.

[Melalvai]

It took me about 2 hours of riding to adapt. But for a couple weeks I still squinted one eye to see into it (to get rid of the overlapping images).

$8 sounds reasonable. I think mine cost $14 plus s&h.

I only use the mirror to ascertain that there IS a car behind me. If I think there is NOT a car, I confirm it by scanning. I think there may be a blind spot with a mirror. It's also really useful for keeping tabs on riders behind me, if I'm riding with my daughter or someone.