I've been trying some basic raw gold farms for single characters, utilizing LFR for old content. There's 3 NPCs, one each for WoD, Pandaria, and Legion, that let you do the LFR version of old raids, with a quick teleport to each boss. You can do each boss once per week per character. It's one of the highest raw gold farms per hour (plus you get transmog from all the boss gear) and the only limitation is the number of characters you have. I try to do separate instances per character, and line everyone up, and run through multiple toons at once, but often I get out of synch, and just manually run one char at a time, but it's still faster than using a single account. WoD and Pandaria don't require any gear, you will obliterate everything, but Legion does take some more time if you aren't geared.

Having the loot a rang saves a lot of time, as does Jeeves and MOLL-E to vendor/mail things. If you have a vendor mount that works in some raids too.

This is something that can be done easily, and you can go afk without worrying about getting killed in case something IRL comes up.

Other than that, doing world quests is always profitable (for both BFA and Legion if you have the time). And once your reputation gets to exalted, you get paragon loot boxes which can have even more gold, so it's a good idea to just do all of them if you can.