I might have exaggerated the edge shape. you can see the effect in real life in some Thermarest Neoair photos. In your use, the large side pontoons will be more rigid than the mattress and will force the edge to be straight. So I don’t think you need to make changes to the original plan. More baffles and curved edge would just mean more work (and less thickness unless you change the internal baffle walls too).
Project sounds interesting! I live in Finland which means mostly flatwater so better speed and tracking are what I’m after.