This WordPress Plugin let you set a wide range of conditions (like minimum/maximum quantity of total items and/or a minimum amount in the WooCommerce cart) to get Free Shipping. You can also limit it to a subset of countries and exclude selected states or provinces inside that countries. Additional settings allow you to specify one ore more product categories for free shipping and limit the maximum cart weight.
NEW: Deactivate free shipping when the normal shipping cost is too expansive. The plugin check the other delivery options and hide itself when the best one is more expansive than the value you specify (thanks to user unikwraps for the idea!)