I don't order Frappuccino's but my go to Starbucks order is as follows: Tall iced coffee with milk with 2 pumps of caramel syrup. I know it's pretty simple, but I love it. You can substitute the caramel for whatever flavor you like. I know that Starbucks has sugar free vanilla syrup.
If I make coffee at home, I chill the coffee in the fridge, then add sugar free caramel creamer and a small amount of sugar free caramel syrup.