In a small saucepan sprinkle the gelatin over 1/4 cup cold water, let it soften for 1 minute, and heat the mixture over low heat, stirring, until the gelatin is dissolved.
Peel, pit and cut mangoes into bite-size pieces.
Place 2 cups of mango pieces in blender; add sugar, vanilla, and the gelatin mixture. Blend well.
Reserve the remaining mango for later.
Transfer the blended mixture to a bowl and stir in the yogurt.
In a chilled bowl beat the cream until it holds stiff peaks, fold it into the mango mixture gently but thoroughly.
Cover bowl and chill mousses for at least 4 hours or overnight.