Upgrade WooCommerce and our WordPress Theme WITHOUT Affecting Customizations

We operate an e-commerce site running on WordPress with WooCommerce, using the MayaShop Theme. We would like to upgrade to the latest version of WooCommerce and the latest version of MayaShop, which works the latest version of WooCommerce. We have made MANY customizations to WooCommerce and MayaShop, and we cannot lose any of them -- we need our site to look and work exactly the same. We would like someone to perform the upgrades on our development server, carefully ensuring that NONE of our customizations/modifications are lost to the upgrade, making sure everything goes smoothly and does not affect the many customizations we've made to the code of these files. Once we confirm everything works perfectly on the development server, we'll need you to make the exact same upgrades to the live server. Not all of the customizations were made "properly" so it may be somewhat tedious to perform these upgrades, and you need to be EXTREMELY careful not to miss any customizations. It is not as simple as just clicking "update plugin" on the admin panel. You will likely need to use a program like WinMerge to compare folders/files to see what's changed. When doing this, we would like you to fix the "messiness" using Child Themes so that in the future we can upgrade instantly without losing any customizations or repeating this process.