You can easily use WooCommerce with Flex theme:
1. Install Genesis connect for woocommerce plugin.
2. Activate by adding one line of code in functions file.
3. Little bit of CSS styling as per your requirements
Reach us if you get stuck somewhere. We are here to help, as always 🙂
FYI, our latest theme Sunshine Pro is WooCommerce ready, out of the box!
Note: If you are looking to accept like same payment directly from users without need to grab too much user info, then you can consider using direct paypal buttons on the website.