Ambrglows, I don't know if you're into this idea, but I just had a visualization while reading your question of a wig made entirely of sequins built on a swim cap. Just a sequin-covered swim cap with many strands of sequins streaming behind. This is probably an out-there idea, but I think it would look cool underwater, like your hair was made of shimmering scales. It would take a lot less maintenance than a regular wig and might be easier to wear.