You can use a harness like a step-in or harness vest for our little dogs - anything secure. I just connect it to whatever harness they are wearing. They make fancy padded car harnesses but mine lay down in their seats so unless we stop EXTREMELY fast or get into a crash, it's the seat that's going to stop them not the strap. The strap is more for safety in a crash or if you slam on the brakes and also to make sure they don't climb OUT of the seat. Trust me, they figure out that they cannot get out pretty quickly.
