I am currently 5'2" and 12 stone. What is the ideal weight to be at for this procedure as I would like a large volume?

Hi,
It's Impossible to tell you without examination but generally speaking the best outcome is achieved in patients with a BMI of about 25. (10st of weight for your height) 
An experienced board certified plastic surgeon should be able to examin you, estimate the volumes of fat and advice you about the ideal weight specifically for you. 

Hello dear!
Thanks for the question and provided information as well.
In general, you need to be physically healthy and at a stable weight, have realistic expectations, be a non-smoker and your BMI needs to be 33 or less.
l recommend you to make an appointment with a board certified plastic surgeon to talk about your goals and anything you need to know.
Good luck :)