You don’t say what model iPhone you have and there are various power banks that will charge iPhones that hikers and backpackers take along for that purpose. Some of the newer models accept magnetic units that attach to the back of the phone. I use AirPods so there is not much power draw off the phone. One does have to charge those too. I’ve never worn them while trying to fall asleep though.

The nice thing about iPhones is audiobooks, ebooks, music, gps navigation, night sky apps, podcasts and so forth. I’d say the camera apps get used the most. Since you have an iPhone just try it at home and see how long the battery lasts and choose the power bank that will get you through.