Simple? or?

The pram type that you posted would work for your purpose. You might also take a look at the Pdracer hull, which is designed for sailing, but would work under oars as well. It is stable because it is square, the full width of 4 feet from bow to stern. Build it with the side flotation chambers for extra security.

Puddle Duck Racer - Easiest Sailboat to Build and Race http://pdracer.com/

Build it with exterior grade 1/4" plywood and paint it with porch paint. No need to go full perfectionist on a boat that you want to use regularly for fishing. If you like it, build another with epoxy and glass sheathing, which will be heavier but will last at least twice as long.

 

Such as this..
Will see how the cutthroat like it in a few months

 

I like it. I often fly fish from a kayak and on windy days, it can be frustrating to maneuver up to a bass or trout spot only to have the wind spin me around while trying to get my range. Sometimes I wish my kayak had more of a skeg to hold me oriented to the water better. You might consider experimenting with a detachable skeg to help track while rowing and keep the boat from blowing around while setting up for those precision casts.

 

Thanks. Yes, I have been using a kayak for fly fishing. One needs 2 anchors on them but even then fishing deep in a lake is a pain. The most consistent person I know uses a small pram, though commercially built. One should be comfortable when fishing. Though will keep the kayak, especially for spinning.