I haveto suggest an older Inazone in the right weight range, with a good bit of closed cell foam to tighten and outfit it correctly. Precisely because it's an older design, it has a different set of compromises that appear to suit the requirements. A lot of my mates started in Inazones and they were perfect for hte job. Playable in G2, but safely paddleable on G4, but a tad risky on the G5 stuff (didn't stop the lads doing crazy-for-the-time stuff in them).
Plus they should be relatively cheap if you can get one in reasonable nick.
I started in a Rotobat, went to a squirt, then to a Whip-It, through an I3-221 to the current Orbitfish/Burn-M combination. For me the I3 was a perfect boat for the requirements until I went 4 stone over the max weight at which point it wasn't safe anymore on G4. I also paddled the UL club's Glide for two years, taking it down a lot of rivers in North Wales ;)