As the sliding rear seat was an option, there aren't too many out there. If you can source one, you'll need to change over all the fixings for the parcel shelf as well as installing the runners, etc. The parcel shelf is a good bit smaller to allow for the seat to go back fully, however when the seat is fully forward, it leaves a gap so that you can see into the boot. I got custom made seat covers for my Panda with an extra flap to cover the gap.
The height adjustment on the driver's seat btw is only the rear end of the seat squab tilting up and down. The whole seat doesn't move so you might be disappointed if that's what you're expecting. Personally I like the tilt as it helps with my back.