How do I get my supply up for pumping!

My son seems totally fine when eating directly from my breast. However when I pump I get MAYBE 3-4 oz between BOTH boobs. But when he eats a bottle he’s not satisfied until about 5oz, and I have to go back to work soon. I’ve been interviewing places, so it’s looking like really soo. I’ll have a job. However I can’t get my supply up enough for him to send him for a FULL day without me. What can I do. I’m thinking about supplementing with formula, which I don’t want to do:(