While writing an essay it’s important to remember that until you hand it in, nothing is carved in stone – not even the thesis.
If, in the midst of researching or writing your drafts, you hit on a thesis that’s more appropriate, or simply one you prefer, use it – just make certain it still fits within the accepted guidelines for your assignment.
Also, when doing research for your essay, try to consult a variety of sources; everything from books, to Internet sites, to TV programs, personal interviews, and magazine articles can be used, so long as the material is viable and appropriate to your assignment.
If you’re worried about citing or keeping a bibliography of non-book sources, don’t be; both the APA and MLA guidelines cover a variety of sources both textual and not. You should consult with your professor or tutor to see which style of bibliography and citation they prefer.