There is some good information about the relative exposure levels to cosmic radiation that one can expect to encounter on this site. They have been doing balloon launches and measuring in-flight levels for quite a while now.
Indeed. But isn't it really only "a thing" for airline pilots, cabin crew and a few unfortunate people at ground level who happen to live/work high-altitude on mountains or somewhere lower down with the wrong kind of rocks ?
Fun story: as part of my physics education we did an experiment on the cosmic radiation with a "radiation" telescope. That were 2 Geiger counters with a logic that only registered events which basically occured in both counters at the same time. That made the observation reasonably detectable and you could "see" the sun with this. This experiment was conducted indoors, just on the top floor of the building. We had about 1 event/second, our bodies would be getting a similar dosis all the time.