Yada

This simple plugin change div html of single product page to always display add to cart button, even if customer didn’t choose some variation option.

WooCommerce Aways Show Add to Cart

Rishi Mehta

This plugin activate add to cart through ajax on varible product. By default woocommerce is not having this feature. Plugin is adding own jquery which is differ from woocommerce default add to cart jquery for simple product.
This plugin also supports sending additional field and other data added by other plugins. It will work with most of product addon and extra field data.
Let me know if you stumble upon any plugin conflict in support forum.

Woocommerce Ajax add to cart for variable products

This plugin activate add to cart through ajax on varible product.

WooCommerce Aways Show Add to Cart vs Woocommerce Ajax add to cart for variable products