Do you have access to Paulownia? It is about 20% lighter than WRC cedar, so it saves about 10% of the total weight of the kayak.

I have built several kayaks of my own design that are a similar size to a Petrel. With 5mm (about 3/16") thick Paulownia strips and one layer of 125 gsm (4 oz) glass inside and out, it is easy enough to get the weight below 13 kg (29lb)

I have one kayak that weighs 8.3 kg (18.3 lb), but that is a racing K1 built from 3.5 mm thick strips and 85 gsm glass. It is fine for flatwater racing, but I wouldn't build a sea kayak quite that light.

I have never considered anything more exotic or expensive than very ordinary woven glass cloth.

I have kayaks built that way that are over 10 years old and they show no signs of falling apart.