I'm completely lost when it comes to a petticoat. The lady who runs Sunday's Bridal where I bought my dress said I need a petticoat that does not tie and spanx. Where do I start and how am I going to know the fullness of the petticoat? Here is a pic of my dress.

Insted of hemming it (I'm just barely 5 feet) she is going to add pick ups to it. Do I just get the fullness based on my preference? Also with the Spanx. . . I need it for my hips. . .should I get a full body one that goes to about my knees? I'm such a tom boy, but I want to look gorgeous for my fiance when he sees me walk down the aisle. Any suggestion is always helpful from you ladies!