Hi,
Before even considering changing versions, I will take the first step of updating your store to the latest version of its branch, namely version 1.7.8.11.
This is fairly simple and will require minimal effort, allowing you to think more calmly about the next steps in your migration.
Currently, the latest truly stable version for use in production is version 8.2.3. Version 9 is not yet ready for use in a project due to the number of bugs and issues it contains.
By taking your time between each major version, you avoid losing too many modules or features, even if the differences between 1.7, 8, and 9 are not obvious to users; it is more at the technical development level that changes have been implemented in the latter two versions.