Set quanitity for STYLE, not size

[pamcasso]

Hi! I'm extremely new to setting up my shop. I hired someone to do this for me, but it didn't end up how I wanted, so I am starting fresh. My items vary in price per size of item, but then I offer several styles of each item. Instead of making a separate listing for each and every style, how do I set up Shopify to offer quantities PER style and not size, but change the price per size. This is how the other lady set up my account, but I might only have enough fabric to make 2 of Style C, but quantities are listed per size AND style.

I would like to be able to select:

Style C (with image changing with selection) BUT then a drop down with sizing and the price change with the different sizes. Is there a certain theme that does this? Or an app? I have figured out how to set up the Style with quantities, but then it gives me a set price for the item. The apps that I choose all will say +$2 if you change the size, but I want the total to reflect the price change, not +$2.