If you like underrated pop music I'd highly recommend listening to some of Peking duk's songs. I personally really enjoy listening to their music because it makes me feel really energetic and ready to start the day :)
New non-mainstream music is my field of study. I curate playlist (on a weekly) basis with new emerging artists (mainly indie rock/pop) and follow other playlist curators that also enjoy discovering new unknown artists. Here are my 5 favourite playlists::
Hmm, I can always recommend you some of my favorite songs. I'm not sure how mainstream these songs are, but here you go! https://open.spotify.com/user/toadmislifeok/playlist/1At8nbkE01xEasjcGuehIg I know this is a mess, this playlist is mostly for my own use whenever I want to listen to certain artists considering this playlist has like 60 songs by select artists. But, maybe you could find new songs from this?