An easy way to develop your thesis is to make it into a question that your essay will answer. What is the primary question or hypothesis that you are going to go about proving in your paper? For example, your thesis question might be “how does cultural acceptance change the success of treatment for mental illness?” This can then determine what your thesis is - whatever your answer to the question is, is your thesis statement.
Most research papers begin with a thesis statement at the end of an introductory paragraph. Even if it’s not a requirement, it’s a good idea to write a thesis statement as you begin to organize your research. Writing the thesis statement first is helpful because every argument or point you make in your paper should support this central idea you’re putting forward.
If you find one really awesome book or journal that fits your topic perfectly, try looking in the works cited/bibliography/reference list at the end of it. This should contain many more books and journals that are about your topic as well.
Your thesis should express the main idea of your paper without listing all of your reasons or outline your entire paper. It should be a simple statement, rather than a list of support; that’s what the rest of your paper is for!