I have the Sportster CS in my 135i and my wife has a Clio RS with the Recaros. The Renault Recaro seats are exactly the same as normal Sportster CS. Any parts you'd need to make them fit would be needed to fit normal Sportster CS seats. The only way you'll avoid that is by paying ~$10k for OEM 'Motorsport' seats (which look great but mount too high).
The Renault base can be removed and the seat mounted using any genuine or aftermarket Recaro slider and either fabricated or Macht Schnell/ VAC floor adapters. The airbag wiring is the same. I used the seat side plugs from my OEM seats.
'Non Renault' Sportster CS don't come with an occupancy sensor so you'd either need to add one or bypass it anyway (mine is coded out- if the crash is bad enough to trigger the drivers airbag the cost of a new dash cover and airbag is no deal breaker for me...)
Your stock seatbelt receivers can be fitted to the Recaros with Macht Schnell/VAC brackets or one can be fabricated easily.
If they are Clio seats you'll need to flip the backrest angle adjuster since the Clio has them inboard of the seats. This is fiddly but not complicated (I had to do one of mine as I had 2 RH seats)
