Using one "Add to Cart" button

Hello:

I am wondering if there is a way that I can use one "add to cart" button and one "Quantity" field where the customer can choose from either a dropdown box or radio button which product they want and add it to the cart using only one add to cart button. Let me clarify a little... I sell medical masks that are all the same except they come in different sizes. Each size has its own stock number. I basically want to have a dropdown box where they can choose the size and it will add the appropriate stock number. I understand how "options" work, however this does not allow me to add a different stock numbered item to the cart. Is there any way to do this? Thanks

JT