I have an ice cream maker (Cuisinart, I think) that you put the bowl in the freezer overnight and it takes about 25 minutes to make soft serve consistency ice cream (which becomes hard serve if you put it in the freezer for a few hours).
I love to use plain greek yogurt (Fage) and add sugar (though you could use splenda) and cocoa mixed with vodka (I prefer chocolate). That turns the cocoa into a chocolate sauce that mixes well with the yogurt to make it chocolate. If you are using 2% or non-fat (or even regular Fage) it has so much less fat that it will get ice-hard in the freezer if you leave it overnight. The effect is lessed with the addition of the alcohol (not enough to taste). You still have to leave it out on the counter to thaw before eating, but not for as long. You can leave out the cocoa (though I still recommend the vodka or other liquer) and just make vanilla or add instant espresso for coffee flavor, or fresh fruit, candies, etc. You just don't add any solid (vs. things that will mix into the yogurt completely) until about 20 minutes into the cycle - so you'd wait for fruit, candies, coconut, etc.
As for proportions, I eyeball it, depending on how much yogurt I'm using, etc. but I use about a cup of sugar for the "big" (35.3 oz) tub.
Make sure you are using the drained greek yogurt and not regular yogurt - it has so much water in it it will end up very icy and not creamy.
The other thing I've experimented with recently is using almond milk and coconut milk - it is amazing.
These all still have plenty of calories, but less than say, Ben and Jerrys or Hagan Das ice cream. Mixins also add more calories than you realize (esp the candy kind).
"You don't have to be perfect, you only have to do better." - Kaplods (3FC Sage)