If you don't want to use corn syrup, glucose syrup is another option (although it's difficult to find any that are gluten free). Golden syrup (Lyle's) is an option, as is honey or maple syrup. Keep in mind, however, that if you use anything that is not corn syrup or glucose syrup, you will need to be very careful about agitating the mixture in the saucepan because the corn syrup is what keeps it from crystallizing.