The problem isn't the thinness of your wrists but accommodating the size of your hands. You need the bracelets to be as small as is possible to squeeze your hand through. With bangle bracelets, your hand is supposed to be what keeps them from falling off.
I'm not sure what "the typical cheap plastic ones" are, but wouldn't they be available in different sizes? Don't they just slip onto your arm?
If you can't find any that are the right size and you only have too big or too small: if the "too small" bracelet can loosely accommodate your wrist but is just too small to slide over your hand, you could cut the bracelet in half and put a hinge and clasp on it.
FF9 cosplay? Hit me up!
2014: Anime Los Angeles, Anime Conji, and whatever else falls into my lap
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