Sweet could be difficult.
I read an article today that suggested vinegar helped lower bs, so, at the exact opposite, I've started using cider vinegar on mine.
Low fat option, so no olive oil.
I eat low carb high fat and make my basic dressing from extra virgin olive oil, white wine vinegar, a bit of dry mustard, pinch of salt and powdered sweetener to taste. Combine the dry ingredients, add the oil and combine until smooth, then add the vinegar and mix well. You can add lemon juice herbs, garlic etc whatever you fancy. I make mine in a jar and store it in the fridge