I have great news to share with you: syncing WooCommerce and QuickBooks won't double your inventory! WooCommerce has an amazing plug-in module that'll find existing items in QuickBooks and update them based on the data that'll be synced - it never duplicates.
We also offer a guide on App support if you're interested in learning more about this. It will help you integrate apps to QuickBooks Online like a champ.
I'm always dedicated to helping, so if you have questions, please don't hesitate for a moment to let me know. Wishing you and your business continued success!