How do I set up shipping for my in-house produced hoodies?

[RogerStout]

I make shirts and hoodies, I don't drop ship we make them in house. 

For the life of me, I can't figure out how to set up shipping. Hoodies are bulky but not very heavy and you can't get very many of them in a box. A USPS large fat rate will hold 3 but the weight limit on that box is like 75 lbs so someone would order a lot of hoodies that would not fit in that given box. USPS is preferred.

If someone could set me on the right path id be grateful. 🙂 Any info you need just ask 

Thanks,