Plexamp is just wonderful, even if the Plex music library management is slightly lacking. Before I moved my music to a Plex server on my NAS I used DoubleTwist's Cloud Player and streamed my own music out of my Google Drive storage. This was 10 years ago, but it did the job well enough. However Plex made all my music available all the time directly on my phone. No moving of files to cloud storage necessary. Easy switch.