Hello Cate,
Thank you for interesting in our EShop Shopping Cart extension. EShop has the Product Options feature which allows you to enter the quantity for each Option Values (Example: Size Small: 3, Size Medium: 5, Size Large: 10, Color Red: 1, Color Blue: 8, etc).
Please read more about it in the documentation at
eshopdocs.joomservices.com/catalog/products#product-options
Hope that this is useful.
Sincerely, Giang