how can I make my iphone headphones louder?

I'm significantly hard of hearing - not so much that I can't use headphones straight with my iPhone SE, but enough that I have to jack the volume all the way up and it still doesn't seem loud enough much of the time. I know there are third party devices out there that I can plug in between the headphones and my iPhone, but they're separate hardware and they require their own batteries.

I've tried looking for an app that will serve as a volume booster (sort of like Boom or VLC will do for my Macbook Pro), but the only ones I've been able to find don't work with Apple's Music app and therefore won't help me listen to the stuff I get through Apple Music.

Is there a solution I'm not aware of that A) doesn't require external third-party hardware and B) doesn't require some sort of jailbreak? I'm perfectly OK with draining my phone battery faster in order to make this work.