Thanks for your totally inspiring note for feminist.com and for sharing your idea with us. Your idea made me think of two things immediately. First, Ophira Edut's anthology, Body Outlaws (formerly called Adios Barbie), which is a collection of essays all related to body image. Second, Ophelia Speaks, which is a collection of girls/young women writing about self-esteem and really responding to all of the books that have been written about their self-esteem. Your book proposal seems to have elements of both.
The first place for you to start is by writing an outline of your project and maybe even include some sample essays or a sample essay. A potential publisher will want to see these to get a flavor for the book. You will need to get a book agent who can help you navigate the publishing world -- they know best what publishers are appropriate and what is a "good sell" right now.
Thanks for your initiative, you inspired me and you will certainly inspire and inform others.