I stuck an inflatable seaeagle kayak seat into my i12s on dry land. The advantage is solid back support that isn't resting on stressed hardpoints. Disadvantage is higher CG (tippiness), loss of some rear cargo space due to the slope of the backrest, and worst is the uprightness of the seatback vs the need to slump back and reach the high pedals. The latter may be curable by letting some out air in one of the 2 (bulletproof) seat bladders. But I'm gonna try the stock seat before further experimentation. Here is a pic:
Why do they put on snaps and zipper instead of corrosion resistant velcro? Anyway I also got their larger "fishing" inflato seat which is super comfy on other craft that can take the tippiness.