Convoys might be a good solution
I understand it's one of the options being considered but it would take a lot of coordination. But instead of the merchant ships spread out over thousands of miles of ocean, they'd move in groups escorted by a few navy ships. Various nations could contribute warships.
Also the sea lanes could be moved farther out, which by itself doesn't help much, but then also banning all fishing boats in those new deep sea lanes, since many of the pirate ships are fishing boats.