You can buy proprietary brands of sugar syrup, or if you'd prefer to make your own, I recommend making a 'rich' two parts sugar to one part water (2:1)...
I nearly always add a shot of vodka to a bottle (500ml) of syrup as a preservative. The resulting mixture would be less than 1%ABV. Is this a good or a bad idea?
I keep my simple syrup in a glass bottle. I make it by pouring the sugar in (2-1), adding hot water from the tap and shaking; it seems to come out fine. Is there any reason that shouldn't work?
If sugar is fine, the water is hot enough and you are patient and vigorous in your shaking, then I can see this method working for rich syrup. It is how most make 1:1 simple syrup.