Make sure that whatever you buy are non-polarising; I bought an expensive pair of sunglasses made by Ray-Ban which, when I 1st wore them, made me think that one of my kx155 nav/com boxes had failed. Fortunately, when I took the glasses of, the truth was revealled and I felt mightily relieved and very stupid.
I have found that an old pair of Ray-Ban Wayfarers, with the arms bent straight over a hot kettle, works perfectly for me.