Does any know of a company that makes a fairly light weight sit-on-top kayak?
Epic V10 Elite
8kg (17.6 lbs). Try not to run into anything, though.
140 Kestrel SOT. 39 lbs. http://www.cdkayak.com/products/template/product_detail.php?IID=136&SID=d807c18825b3aab32de8858df0f2fed7
Depending on usage, you might consider a pack canoe, a dichotomous grouping of watyercraft.
The Ultra lights tend to run ~ 10.5 feet to 12 feet in length, have minimal outfitting and are built to carry, which makes them somewhat fragile at 12 to 18lbs. Look up Compass, GRE, Hemlock and Hornbeck on the web.
The Trippers start at 12 feet, have more complete outfitting, [seats, footpegs, backbands], and are built to take tripping abuse which makes them somewhat heavier; 20 to 25 lbs. Look up Bell, Placid boats, Vermont Canoe and WeNoNah.
All this is predicated on what your knees look like. Here in Lake Placid, the Lycra Board, an elected committee that determines if individuals will be allowed to wear Lycra in public also sorts the citizenry by knees. Those with ugly knees are forced to use kayaks.
My Wave Witch Horizon is 12.5’ and weighed 28 lbs with 3 hatches and a rudder.