... a quick market product research about PFD/buoyancy aids that are compatible with a seat or waist harness:
a) PFD with a high harness hook hole:
b) PFD/buoyancy aids that are compatible with a waist harness:
O'Neill Superlite USCG wake/waterski vest (4 buckles, no front zipper, bottom buckle may be left unclosed to ease access to high harness hook) http://www.oneill.com/#/men/europe/c...t/black_white/
Caution about so called "kite vest" or "impact vest for kitesurfing" : they have very low buoyancy/flotation capacity, much less than 50 N:
c) kayak-designed PFDs :
These kinds of PFDs are fine with a low hook racing seat harness type. Problems I see is that they are too bulky to be worn over a waist harness and the presence of a front zipper might severely hinder/reduce the free access to the high harness hook when windsurfing.