How to track own theme changes for future reference – not full developer style

Hi, I am looking for a method/app/approach to make sure I can track the small fixes I make in the theme code so as to make sure I can upgrade or change my theme easily and debug problems.


We are moving from Debut to something else, and this time I want to do it right to ensure I can follow my small code changes and save them when updating the theme.


Most of the changes are very small, but required, modifications that cannot be done with the landing page editor apps, like adding mandatory terms and conditions to the cart or similar. Having the theme developers do it would be the easy, but way too costly solution.


Also, I am not a developer, so I am not looking for a full theme development solution involving GitHub etc. etc. which will take too much tech work for this limited purpose, since I want to spend my time on running the webshop itself, not doing command-line work.


Any ideas how to handle this?