[Dark Skies]

There are plenty of Porsche baby seats on ebay - found them when looking for regular seats. They are generally fastened to the seatbelt anchors hidden (if yours doesn't currently have rear belts) under the rear seats. There's an anchor either side of the hump (in the middle) and one under the carpeting roughly underneath the rear speaker. The foam padding underneath usually has holes pre-cut so you can generally get an idea of the location by prodding with a thumb.

It's no big deal to lift the rear lower seat. It's just glued on the chassis base and clipped at the top underneath the upper backrest. You can see the clips if you lift the carpeting under the rear hatch. Whenever I've renewed the rear seat base I've just used carpet spray adhesive to glue it back down again.

The upper part of the seat most likely utilizes the upper rear seat belt mount - located on the rear quarter panel trim and generally blanked off with a plastic screw plug.

Those clips at the back of the rear seat are no good - they're for the luggage net and are made of plastic.

A morning's work to do the whole job I reckon.