Get a set of TEPS II sunglasses from UK sports eyewear
http://www.uksportseyewear.co.uk/product.php/38/kit-car-glasses-biker-glasses
They do loads of different lenses for them too - clear, amber, Iridium Red, Polarised.
I bought a pair of these last year they are good. Can be worn as glasses or wrap around goggles and cheaper than your sun visors