Send a mail when customer chooses a product variation

In my e-commerce site based on Woocommerce, I sell clothing products all available in different standard sizes (for example: 44, 46, 48, 50, 52, 54) and then made-to-measure. I need that when a customer purchases any product by selecting the “made-to-measure” variation, the system sends the customer, in addition to the order confirmation email, also an email with instructions on how to take the measurements that the customer must have the possibility to respond in order for us to avoid to send manually this mail

Thans to anyone who will help me