http://www.learningaboutelectronics.com/Articles/Voltage-doubler-circuit.php
The size of c1 should equal to c2. Going from full bridge rectifier to a voltage doubler means you get a half wave rectifer.
This means the size of your capacitor needs to doubble for same ammount of ripple compared to a full bridge. Further more its effectivly quad cap size for same ripple because you need two capacitors to doubble voltage.
https://en.wikipedia.org/wiki/Ripple_(electrical) 1.1 filtering
voltage ripple equals to Current/ (Freq*cap size)
in full bridge the rate at which the caps can charge is doubbled, the transfomer is 50hz and effectily charging at 100hz.
Half wave means it charges at 50hz.
Because we now have two caps they will both charge and discharge at same time, the fourmula only monitors the votlage ripple accross one capacitor not two.
Because the supply draws equal power from both caps they discharge equally, and because each cap holds half of supply voltage, the voltage riple seen is doubble.
Imagine a voltage supply with 1 voltage ripple you put two in series for doubble volts now you get 2 voltage ripple, same in what is currently happening.
This means the actuall ripple current is 2*Current/ (Freq*cap size)
We know the current and frequency, now we can find a suitable cap size.