My solution
Hi All,
I can't comment much on bi-focals as I have only ever had one pair and they were on a special prescription specifically for working at my computer and reading at my desk. All I can say is that I disliked them. I found the line between the two focal distances just too irritating. With bi-focals the reading section always has a 'sweet spot' that is just below the line. If you miss that then you don't see what you are reading quite as well.
In 2005, I returned to flying after a break of many years. By this time I was in my mid-sixties and regularly wearing varifocals. At that time it seemed to be received wisdom that one should never wear varifocals for flying under any circumstances. In fact, I used my varifocals without any difficulty whatever. The only caveat was that if I wanted to look at something that was situated well over to one side, I had to turn my head to look at it rather than just my eyes in order to avoid optical distortions.
Since then however, varifocal technology has moved on. There are now varifocal lenses where the whole upper half of the lens is thoroughly usable distance lens. You don't have to turn your head to avoid distortion anymore. I think these are, however, a more expensive ultra-thin lens and may be more expensive than the ordinary bog standard lens.
Eventually, I began to use two pairs of vari-focal spectacles for flying. Both had thin, metal frames (for wearing under my headset) and the latest varifocal lenses in a big 1980s lens style, which are anatomically better than the current small fashion size lens. One of these pairs had graduated tinting so that the upper part of the lens had a dark, sunglasses-density tint, which gradually reduced to nothing at instrument panel reading level. The other pair were clear plastic lenses. Together, these worked very well indeed.
Broomstick.