I now use a modified bike DH helmet.
This Kenny helmet seems popular in jetski.

I have cut the front and replaced the cheek pads for water tight foam.
The idea was to use it with some kind of minerva or a neck protection included in the impact vest (like in motor bike sports).
So far I use it by itself. As it is bigger than windsurfing helmets it doesn't go into the water as easily and has protected me nicely from backlash. The head doesn't go back when you fall backwards. It "stops" at the surface.
Protection on the side is good also as I have in the past nearly fracture a cheek bone when the sail flew around and caught by head poping out of the water...
Of course I also use my free-fall harness hook.
It is also of a flashy color and this has helped me in July. I had broke the mast and altough I had a phone to give alert (and gps location), the rescue team didn't and had a hard time spotting me until they saw me waving my bright helmet farther out than they thought...