Hi @pierovm!
There is no option in WooCommerce core to add a checkout button on the product page after adding it to the cart; this would require a plugin or custom coding, as you remark.
Since custom coding is outside our scope of support, I am leaving this thread open for a bit to see if anyone can chime in to help you out.
Searching, I couldn’t find any plugin that could do what you want to achieve exactly, but I found some code that could be helpful to your case:
https://wordpress.stackexchange.com/questions/271612/add-additional-checkout-button-next-to-add-to-cart-button-in-woocommerce-pro
For additional assistance on this topic, we recommend getting in touch with one of the customization experts listed on the WooCommerce Customizations Page.
Also, you can visit the WooCommerce Facebook group or the #developers
channel of the WooCommerce Community Slack, you could find help from the community of open-source developers for WooCommerce that hangs in there.
I hope this helps!