Drupal 8 Commerce 2
Our site sells fabric by the roll, not by the yard. Each roll is a unique one-off. Due to inconsistencies with color, we offer samples. It’s unfeasible create sample Products for each roll Product we post. What I envision is adding a "Get A Sample" link or button to each product’s page that would, when clicked, capture the product’s ID, then add a sample with that ID to the Cart.
I’ve been playing around with Field Tokens, Commerce Add To Cart Link, and Direct Checkout by URL but have yet to get anything to work.