Considering the fact that you have a single product, I would have recommended Magento but it's way too much for what you need. WooCommerce is a great option for that.

I currently work with Shopify and Bigcommerce. Both have come a long way and have a great selection of apps that allow you to do all sorts of things. Depending on which plan you're on, Shopify does allow you to change a lot of code within your site.

Hope this help.