Does anyone know what (if any) other seats would be a direct fit into a Superb II? I'd like something with a bit more bolstering on the sides. Wondered if the more sporty Audi seats might? 

Audi A4 and A6 are a completely different platform to the Superb, so it's unlikely the seats from those will fit. Passat 3C is the same platform so you could see if there are seats around from the R36: they should fit the Superb. Given the platform's origin as an extension of the Golf Mk5, seats from that model may fit too.

I find the superb seats too bolstered if anything

Thought as much. Quite fancied some S6 seats or something. Can't really go aftermarket because of the airbags!