If you must use prepared sauce from a jar, get the Classico Tomato and Basil, then simmer for about an hour, stirring often. You can have it as thick as you want. My gripe with prepared sauces is the sugar they add to them. This variety of Classico doesn't have added sugar.
I add the spices my grandma used to use: cinnamon, clove, sweet basil, black pepper, and cayenne pepper. Delicious.