How to downgrade to OS X Yosemite 10.10? (Have not yet upgraded)
Now I am curious about upgrading, but I would like to find an option that would allow me to roll back to my current set up if I did.

You can use Internet recovery to rollback to the factory installed version of macOS. From the Apple Support document, How to reinstall macOS from macOS Recovery:

macOS Recovery makes it easy to reinstall the Mac operating system, even if you need to erase your startup disk first. All you need is a connection to the Internet. If a wireless network is available, you can choose it from the Wi-Fi  menu in the menu bar. This menu is also available in macOS Recovery.
Shift-Option-⌘-R
Install the macOS that came with your Mac, or the closest version still available.

Do note to keep a Time Machine backup of handy. Once you have restored the original OS, you can recover data using the backup. Also, it's best to test the sanity of the backup before actually reinstalling the OS.