Yeah I'd agree its much easier to refurbish the original ones.
The only non-standard seats that ever fitted well enough in my defender were a pair of old bucket seats from the rally car but even so they were'nt practical for daily use.
Another one here for RX8 seats. I managed to pick up a set of full leather RX8's in genuinely near pristine condition for £150 from a great seller on GumTree. I plan to make my own seat risers and fit in the New Year. + not too keen on the silver plastic triangles...thinking of wrapping a piece of matching reinforced leather around the plastic moulding and refit with black button hole screws