Forgive me if this has been asked before. I was unsure what exactly to search for.

Let us say I sell shirts and pants. If a customer orders less than four shirts, I would like to give them a flat shipping rate. If a customer orders less than three shirts and a pair of pants, I would also like to give them a flat shipping rate. If a customer orders anything else, they can choose between my normal shipping options.

Is there a way to set that up?