Offline Music Players for IPhone

I switched from Android to iPhone a while back.  I am going on a long trip and will be doing a fair amount of offline listening.  I have some files scattered about in various parts of the OS.  My Android phone had a great music player but these same apps don’t seem to be available in iOS.  I don’t mind paying a few bucks to have a decent app minus advertising.  The ones in the Apple Store let you try them for about 5 minutes before asking to purchase and that isn’t long enough to decide if it meets my needs.  I don’t want anything that pushes new music at me as the purpose of this is offline listening.  When I’m online I will use my regular streaming service