I'd seriously consider switching to a waist harness. The agility you have when gybing and getting the board planing and in the water when water starting makes such a difference to your sailing.
I use short harness lines, I guess a product of a waist harness and a bit old school (mind you I seem to recall old school was long harness lines)
How does a waste-harness help with water starting and gybing when you are out of the harness when doing these things?
I use a seat harness, but one of those combo type harnesses that runs a pretty high hook (though I adjust it fairly low), but still has leg straps to stop riding up when sitting in it. I find it no impedement to water starting or gybing... and I find it better for general locked in cruising that is most of my sailing than a waste harness.