I’m selling on both Shopify and Google Shopping while having litcommerce sync orders for me, and it is running smoothly I guess. This feature is sort of easy to use and convenient; it syncs all my orders from both Shopify and Google Shopping to my litcommerce dashboard and I will manage all my order information there. I used to route all orders to my Google Shopping store as well after the orders arrived at my litcommerce dashboard, but these days I only stop at the dashboard.
I remember they do support Wix and BigCommerce too. Just pick Wix as your main store and Shopify and BigCommerce as sales channels during the setup.
I have just upgraded my pricing plan and I think their services don’t cost too much compared to other tools. Just chat with them and see if they have a suitable plan for you.