In reply to Hooo:
Thanks to all for the advice - much appreciated. I will probably go with prescription long distance sunglasses (maybe add some side pieces, and take the glasses off for reading the map). I will also try the option of contact lenses + cheapo reading glasses (I'm quite keen on this coz I like contacts except for not being able to read). Will also look at the "cocoons".
just to respond/explain about the other good suggestions: 1) varifocal contacts worked at first but then didnt work (or made me feel pukey!) as the difference between my long distance and reading prescriptions got worse; 2) contacts with different prescriptions in each eye worked at first but then didnt work as the difference between my long distance and reading prescriptions got worse.
Thanks again to all.