I'm trying to figure out how to configure the following options for customers. I sell fountain pens and ship using usps flat rate small box. That works perfectly in the US. I have flat rate small box as my default box. But internationally I would like my customers to have the option to choose first class package international shipping OR Priority small flat rate box. I'm losing sales due to not being able to offer the first class package option. However most prefer priority and the flat rate box is cheaper then my own packaging. I've tried setting up zones (one for domestic and 1 for the rest of the world) but I'm not getting the result there either. And I'm not able to add the same item to both zones, what's that about? Please help. I'm not adverse to using an outside app connected to shopify, but it needs to give my customers the options I'm needing. So far I can't find that.