Optimal way to pump?

Hi all! I exclusively breastfeed my 7 week old son. The week of May 4th I'll be returning to work. I work at the childcare center he will be attending and he'll be in my classroom. However I'm the lead teacher and probably wont be able to nurse him while on the clock. I'll only be starting off with 5 hour days so he should only need to eat once or twice while there. But how do I pump most efficiently? I occsssionally give him bottles of breastmilk and he'll suck down 3oz and be content. But I can pump from both sides for 10 minutes and get 2oz, sometimes less. I've read it's very normal to get less when pumping because pumping is less efficient than a baby nursing. But how am I supposed to pump enough milk for when I'm working? I have 2 older children (ages 4 and 2) so I dont have a ton of time to pump to begin with. I have a The First Years pump. It was super inexpensive and I'm thinking I need to buy a better quality one, but I need to save up the money first.