Sporty's sell glasses with no side pieces, they clip to the brim of a cap and fold under the peak when not required, also, if you have a favourite pair of sunglasses, and the old age trick starts to bite, most U.S. drug stores, Rite-Aid, Walgreens etc. sell small semi-circular plastic lenses in every useful dioptre value from 1.0 thru 4.0 that you just stick on to the bottom of your sunglass lens, and Hey Presto ! you have a pair of custom made prescription sunglasses for a 100th of the price that the optician will charge, can increase the strength easily too, as age progresses. Have only located them in the U.S. tho.
Beware of the colour, too. Blue-Blockers - those yellow jobs - make it impossible to read the charts ! I find B.B's dangerous for driving, too, they make everything monochromatic, and coloured cars that I never see come leaping out of side roads at me. Like watching an old black and white movie.