In the original game, the balls bounced always to a specific height: the biggest balls would bounce to a certain height, the middle balls to another and so on. This is why, instead of using physics, which probably would not be that accurate, I decided to use Animation Curves. 

 

For this, the Ball script evaluates an Animation Curve and positions the ball vertically based on it. This way, there is also a lot of room for easy tweaking.

The Animation Curve only represents half of the bounce so that when it reaches the end, the read value gets inverted. This way the curve will always be symmetric and prevents strange behaviors.

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The curve can be rescaled in time and value and the movement will adapts to this.