How do I allow for T-Shirt orders that are different sizes?

I would like my customers to be abe to select a specifc t-shirt size for multiple shirts. Right now you can pick a t-shirt size and quantity, which works if you are getting 2 of more of the same size shirts. I am looking to accomodated the customer who wishes to purchase one small shirt and 3 medium (as an example). 

Thank you for your assistance. 

I think a better idea would be to do something like this http://form.jotform.us/form/41247461459155  or you could reverse it the other way around and have the Product be the color instead. Just one thought on a way that you could do it.