There is a lower cost of upgrading to paddles for the cars that still have the buttons. Instead of replacing the entire switch with a pricey MB part, this approach is to keep the switch you have and just replace the button with a custom made paddle. It takes about 15 minutes to switch out the buttons to the new paddles and there is no need to remove the steering wheel or any wiring or more. Simply pop out the switch, remove the button, and snap in the new paddle. Slip the switch back into its place and move to the other side.
The paddles are made and sold by a couple of enthusiast in England and ship anywhere. It took about 10 days for me to get mine on the east coast US. Check them out at G-paddles.com and on YouTube: