I make it the way you do. Just add the simple sugar to taste. I like mine less sweet.
A local restaurant uses this method. They have the jars all over the walls. They also use Everclear which I did until ot got too expensive.
https://gizmodo.com/how-to-make-the-best-limoncello-youve-ever-had-1533528095
Directions:
Pour vodka into a clean glass jar.
Wrap lemons in cheesecloth and suspend over vodka (using the twine to secure them).
Seal tightly, and let sit undisturbed (in a cool, dark place) for one month.
After one month, discard lemons, then add syrup and the fresh zest of two new lemons.
Let sit for 15 minutes, and strain through a fine mesh sieve (or more cheesecloth).
Chill and then drink up.