Is it right to file I130 instead of I864 for my fiancé if my income is not enough and I have to have a co-sponsor?

I-130 is for a family-based petition and not fiancee visa petition. I-864 is affidavit of support. They are completely different forms.

You cannot file I-130 for a fiance. You can only file a Form I-129F for a fiance, not an I-130 petition which is filed for spouses. before filing any form with CIS read the instructions carefully

The are separate forms. Both must be filled. A joint sponsor would file an i-864 in addition to your own i-864.

Unless you are already married to one another, you cannot file an I-130 or I-864 for her because those forms are only applicable to spouses. The correct forms to use for a fiancee petition are the I-129F and I-134. If you are legally married in the future, you will need to file the I-130 petition first and then the I-864, regardless of your income, after the petition has been approved and transferred to the National Visa Center for consular processing.