I have never been a big gold hoarder like alot of people. I also refuse to buy gold. It always seemed sketchy and I wont pay money for something i can just go do.
By far the best way to get gold in my experience has been old raids. ANY expansion works; However, The later expansions are far more rewarding. I recommend downloading Atlaslootenhanced addon so that you can see what sort of pets the raids drop too. That way you can optimize pet drops and sell them. Not to mention you get a chance to get old raid mounts or grab some glory achieves while you're there.
As far as garrisons go... yeah gather professions are ruined if you are still paying for ore or herbs.... you are reallllyyyyyy lazy.
I get about 500~gold a day from collecting missions(once a day usually) and just selling all my lvl 3 scrapyard goodies.
Also if you did dungeons to 100 and no questing go do the questing. i started with about 4-5k gold at start of WoD and once i hit 100 i had about 18k just from questing