Pour boiling water into a blender. Carefully add the sugar-free gelatin. Close the lid and hold it down firmly. Blend on low speed for about 30 seconds, or until the gelatin is completely dissolved.
In a separate measuring cup, combine cold water and ice cubes until the mixture reaches 1 1/4 cups. Add this ice-water mixture directly to the dissolved gelatin in the blender and stir gently until the ice has partially melted.
Add the plain non-fat yogurt to the blender. Secure the lid once more and blend on high speed for 30 to 45 seconds. The mixture should become smooth and frothy.
Divide the freshly blended fluff evenly among 5 dessert glasses, small bowls, or ramekins. Place them in the refrigerator and chill for approximately 30 minutes, or until the fluff is fully set.