I don't want to buy a new iPhone battery. Can I rollback to a previous iOS? Or is jailbreaking useful?

What might be the downsides of going this route? My iPhone 6 Plus has been slow and buggy since updating to iOS 11. The main thing I'm worried about are my podcasts. I have a queue of about 100 shows to play next, and I've subscribed to dozens of podcasts. I listen to them when at the gym, on road trips, and at work. Can I go back to a previous iOS or jailbreak my phone without disturbing this?

Hm

You can't rollback to a previous version at this point. Jailbreaking wouldn't help either. I think getting the battery (if it is the issue) should be the best option.