How to get a semi-conventional loan?

[Joshua Cetnar]

I got pre-approved for a mortgage, but it isn't enough for the house I want to buy. It was calculated using 28% of my monthly income. I'm assuming they're just following the rules so they can sell it to Freddie Mac. I'm planning on renting out rooms to help cover the mortgage and I can afford a larger purchase, but obviously the bank is held to its rules. I'd like to get a traditional 30 year fixed mortgage if that's possible.

Where should I go next? Credit Unions? Other banks? It's not a straight-up investment property, and it is my first home purchase and a primary residence.