Help-I know there is an answer, I just can't find it! How to have different inventory management

I am not the first to struggle with this, but I can’t find the solution. I appreciate your help. We are starting a graphic t-shirt business. I need to track the inventory of the graphic design seperately from my apparel inventory. How do I do that? I have tried apps to create bundles of the design and t-shirt so it was pulled each time an order was placed, but it would not pull the graphic design. I am lost and frustrated!