You can just move the main game folder (that is installed in Program Files) and just leave the Documents folder alone.

The game doesn't care where it is run from, it only cares that the structure is intact. The only thing it does active look for is the Documents folder so just don't touch that and you can move the game off your SSD or wherever you want (if you're worried, copy it instead of move it and try running the ffxivboot.exe from the new location, it'll work just fine then you can remove the old files).