Blue Ox and Roadmaster both make base plates for Smart cars. I installed a Blue Ox on my VW new beetle and I'm confident it is strong enough for safe towing. I got a Blue Ox Anenta II tow bar on Craig's list for less than a third of new price. It is adjustable, so hooking up is much easier. A non-adjustable tow bar must be exactly lined up to connect.
Even though you were told you don't need a braking system per Florida law, be advised if you go out of state you must abide by their laws and you might need brakes for anything over 1500 lbs.
In addition, I think the Law of Physics trumps Florida laws. Do you really want even a Smart car pushing you when you have an emergency situation or mountain descent? Take your car in a flat parking lot, push it as fast as you can, then try to stop it. Now imagine the speed is 60, not 5-6. Supplemental brakes are cheaper than body work on a coach or the life of a pedestrian.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI