It sounds like you need the full I-864 ... and possibly a joint-sponsor.
PS You can never go wrong by doing the full I-864 ... which we always use. The EZ isn't all that easy.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
I always use the 864, but if you do not meet the income requirements it does not matter which form you use because you cannot be the sponsor on your own. You will need a joint sponsor or a second job. This is one of those times where consulting with a lawyer before you file something that gets your case denied is a good idea.
If you do not meet the income requirements, then as stated in the instructions you read, you cannot use the I-864EZ and must therefore use the I-864.
You should retain an experienced immigration lawyer to review all the facts, advise you, and handle the case. You can find one through http://www.ailalawyer.com.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.