What can I do, representing myself, to ensure that I am granted legal custody?

You really should have legal representation on this; much is at stake here. If money is an issue, see if you qualify for Legal Aid or see if they can recommend someone to help you. Also, check if there is a law school nearby to where you live; they typically run free/low cost clinics that handle these type cases. Contact the local Bar Association in your county; they may have a list of attorneys who will take your case "pro bono" (for free) or at least for a reduced fee based on your income/circumstances. Additionally, google women's support groups in your area, they can usually provide a list of attorneys who can help. Finally, contact your state's Department of Social Services, they may be able to refer you to free legal services.