It is very difficult giving accurate information without seeing you, but, I will do my best.
As your hair is fine and you like your curl result/volume it gives you should look at having another curling technique in the curl process. ...More >
I would not use a rod or perm roller. I would pin curl wrap small sections in opposite directions each time to give a natural textured look. Apply a small plastic grip and apply lotion.
By applying this curling technique you will get more volume easier, as the curls work against each other when styling giving a softer more natural look than being wound around a roller.
Give your bang a soft curl or movement also as this will add to the finished look. Do not allow it to grow too long as this will make your styling much harder. I would grow it just below jaw length, BUT DO not have your perimeter outer shape strong club cut as this will emphasize your square face shape. Instead have disconnection around the perimeter (outer shape) that falls longer to give you an unstructured shape on the length. With movement this looks fantastic.