I have put off making a recipe for this cocktail for a while simply because there are so many disputed variations! People disagree on many things, particularly fruit or no fruit. Me, I like the fruit. Orange and cherry muddled in. Sometimes I even use orange bitters to add more orange flavor. Some people use lemon instead of orange. And some people make it completely without fruit.
Instead of a sugar cube and water, feel free to use simple syrup. It will make the dissolving step easier. However, I find that the sugar dissolving is a good measurement for stirring the ice enough to melt/dissolve it and increase the water content of the drink.
Really, as long as the whiskey is good, whatever variation you go with is going to be good. It just comes down to figuring out what it is you like. I know my dad makes a very “untraditional” Old Fashioned that is quite delicious (and deceptively alcoholic!). Don’t let the fear of breaking tradition scare you away from experimenting!