Radio buttons are more friendly than dropdown selects. This plugin will help you have a better UX in your WooCommerce site, as your customers will see all your variations without having to click on a dropdown.
The radio buttons will be toggled dinamically so your customers won’t be able to choose non existent variations.
This plugin may not work out of the box with some themes. This is due to a theme having its own template for variation selection (single-product/add-to-cart/variable.php).
To make this plugin work with a non compatible theme, a child theme has to be created.
Then copy plugins/wc-variations-radio-buttons/templates/single-product/add-to-cart/variable.php to themes/your-child-theme/woocommerce/single-product/add-to-cart/variable.php
Source code and contributions at github