I am seeking a suitable fabric to make some gear. Basically between Lycra rashie and Hydroskin in weight and just as stretchy and able to get wet. Would need a few yards, color not too important.
Try this: http://www.seattlefabrics.com/stretch.html
One of those stretchy polyesters should be like rash guard material. You can order samples to help make your choice.
They also have neoprene, but nothing thinner than 2mm, so probably thicker than you want.
Polartec Aqua Shell
It’s a bit pricey, but sounds like what you have in mind.