Family co-signer in exchange for % equity on first property

[Anthony Saunders]

I am looking to purchase my first property in San Diego. Ideally a Duplex so I can live in one unit with my partner while renting the other. I've accumulated a substantial nest egg after college and paid off all student loan debt. As it stands My DTI is at 68% In order to qualify for the loan amount I'm seeking, I need to bring that down to 48%. My partner provides stable income that would get my DTI in range. However they are not a part of the loan deal. The lender suggests asking a parent to co-sign.

Which leads me to my question. I intend to approach my mom, with an offer for % equity in exchange for a co-sign on the 30 yr loan. I’m a fiscally responsible, and just shy of gaining approval on my own. She is in a strong & stable position to easily increase my purchasing power. 
What % equity on your first investment property would you offer your mom?