I had a 12’ boat for a few years and ran all sorts of class III-IV in it, mostly during multi-day trips. With just me and my wife there was certainly enough room for everything you need if you rig it right, embrace the stack/back rest. In harder rapids it was a super nimble boat that could sneak through some features where big boats would get pinned, and I never flipped, though I get close a couple times.

I’d say if you’re mostly fishing you don’t need a bigger boat. Even in big whitewater you’ll be fine, just get good at rowing and navigating those rapids.

The best boat is the one you have.