Extending blouse into dress

I'm planning to extend the blouse into more of an a-line tunic/dress to wear over leggings. Any advice on how to do this would be much appreciated. I think if I simply extend it at the bottom it will be too wide. Does this mean I have to slice it either across or downwards and lengthen and make narrower? Or am I over complicating it and I could just add to the bottom? In reality I'm not going to make a muslin, but I don't want to mess it up as I will be using some of the new Alice in Wonderland lawn... Thank you in advance peeps!