Thanks Iggypop
I tried that though, and didn't help much.
I'm quite long, so when it slips up, my bum goes down and hits the waves (

), so I would put on a very short harness lines, and the whole geometry would be skewed. I had to go to the seat harness, and all clicked after then. (for windsurfing)
Now a waist harness with straps, (thanks weebitbreezy) that sounds good.
I knew of a combo waist/seat by Flying Objects - with a full seat, and riding high, but after trying it on...nothing wrong with it, just didn't feel right.
I'll have a look at the one North and Ocean Rodeo. Thanks