Quantity Discounts for Sets?

My wife sells "nursing pillows" that come with zippered covers. Basically the way she has been pricing her product line is $29.99 for the basic pillow, $12.99 for the zippered cover, but if you buy 5 or more SETS (and other discounts at 10, 25, 50 and 100) you get a discount. BUT if you only buy say 10 basic pillows there's no discount, nor is there one if you buy 10 covers only. They must be bought in sets. On top of that a typical order would be for 5 pillows and 5 seperate, different cover patterns.

How can you "program" that pricing structure into ZenCart?

The Better Together add-on might work for you.