Ortlieb Ultralight Bike Mirror - convex -5" tall by 2" wide at top (narrower at bottom) - 58 grams - $25 to $30 depending upon vendor - available at the following vendor and elsewhere:

https://www.modernbike.com/ortlieb-u...nd-bike-mirror

I have this mirror on two bikes - good visibility and generally stays put because it is so light. The knuckle joint on the arm is very effective. The plastic band attachment to the bars is good - however, you can't crank the plastic band down - will just strip the plastic teeth - but because the mirror is so light it doesn't move (much) on rough roads - a little electrical tape will keep it rock solid.

Mounting it just below the brake lever allows me to ride the hoods and the lower/mid drops without interference. I can see the mirror clearly when riding the hoods, tops, and drops without having to move my head.