WP Inventory Reserve Cart
If the one and done does not work for your website, get the reserve cart add on and allow your users to add items to their cart before checking out. This will ensure they don’t get repeat emails as they use the site and make it so that they do not have to submit the form every single time. They simply add all the items they want, and then checkout. Simple and easy. It is exactly like shopping cart functionality without taking the payment.