We had the same problem for one of our clients, and got inspired by the script from @asleischow, and created our Extra Ecommerce fields attribute (by BRIX Templates), that allows you to add as many extra fields as needed, and the only thing you need to do is add a single attribute.
It’s open source, free forever, and you can implement it in 5 minutes or less.
If you want to see the tutorial, take a look here: Extra Webflow Emmerce fields by using the BRIX Templates attribute on Webflow.
If anyone want any extra feature on it, just let us know and on the next article update, we will add it ;)