Based on my estimations of my body tallied against the information on the sizing chart, coupled with my own personal crusade to buy locally whenever possible, I bought a Diva Cup (size 2) from my local health food co-op.
And people, it was an unmitigated success!
By some stroke of luck, the Diva fit me well and I had no stem-poky-problems. There were a couple times when I couldn't get the cup to open, but a removal and re-insertion did the trick. The 7-fold works much better than the other folds I tried (C-fold and punch-down--I didn't feel like trying anything too fancy right off the bat). The only time I had any trouble with removal was the very first attempt on my pre-period dry run. And I think that was largely due to me trying to figure out how to maneuver my long-ish nails around the cup without injury.
In another stroke of luck, this was one of my Bad Periods, which I have a few times a year: near-debilitating cramps (which keep me awake at night), heavy flow, exhaustion, headaches, nausea...the whole nasty deal. But I think the cup was easier on my body--and it certainly kept me somewhat interested and entertained! So much better than feeling a little repulsed by the numbers of tampons I've added to landfills over the years. I did use a pantyliner every day (and I was grateful for that), but I would've done that with tampons, too. I don't imagine that habit will change, although I might move to washable pantyliners eventually.
Thank you so much, menstrual_cups LJ community! You all are the bomb. I could not (and would not) have done it without you.