usability – Product Purchase flow with Add-ons

I have a page where the user can purchase a digital product by itself, in a three pack, or in a five pack. The complicated part is that the user may also purchase add-ons for the products in the pack, but in a separate quantity.

eg. The user may want to buy a 5 pack of the base product, but only 2 add-ons.

Is there some design pattern that solves this problem? Is there a better way of illustrating this?

I’m stumped ..

My current wireframe : /