Personally I feel like samurai and red mage are probably the least complicated for dps. They have pretty straightforward rotations, even at 70. I'm not sure if you have to have Stormblood to have them unlocked, though. Of the original DPS, I'm not sure which would be the easiest. All of them got a lot of stuff added between level 51 and 70. Black mage takes some getting used to at 60 when you have to learn how to keep Enochian up for Fire IV rotations, for example. But other than that, it's not that bad.
Also, you might try out healing with white mage. Healing itself can be stressful but the process isn't terribly complicated.
Tanking as a paladin is another option. There's not really much to the rotation until 70 and that's if you're trying to maximize your dps output while tanking.
I think I put my character name in the general topic, but mine is Senah Kha if you want to try and look me up in game. I haven't been on much myself recently but I probably will at least tomorrow and Wednesday. I have all of the combat classes at 70 so I could take you through dungeons or stuff if you needed help with that. You can run dungeons unsynced so that might make it a little easier to learn the new bard stuff if you want to keep going with that.