You can use full fat milk for a richer coffee for sure!
Do not add more water than two to three drops. I heat little water in the microwave and then drip it into the coffee and sugar, just enough to wet it.
I have seen some recipe adding cream. If you wish, you can top your coffee with whipped cream and to make it extra decadent, some chocolate sauce as well! Since I have enough to my waist line, I would avoid them! ;)