I actually found that podcasts were better to keep me going than music, although ones that were funny could be an issue if I started laughing. The NHS Couch to 5K app running over PocketCasts was okay because somehow Android (so I guess iPhone might be the same) would tell it to pause while the app announcements came in so you don’t miss any of the info. (I say this because I played one via the music app one time and then it just lowered the volume so that was frustrating.)
Anyway, I used it to work through some of the free Dan Carlin’s Hardcore History podcasts that are like 4 hours an episode. They worked quite well chunked up, but equally Criminal is a great podcast where each episode is usually about 30 mins.