I used when I tried Spotify about a year ago. I used https://www.tunemymusic.com/ yesterday for Deezer and it's free. Seems to support nearly everything.Import Google Play Music playlists and favourites tracks, albums, and artists to Spotify in one go. Follow this tutorial and move to Spotify in just a few steps.soundiiz.com
Give that a try with Spotify. I did something similar when I switched from GPM to Spotify a couple years ago and it was seamless.
Problem is Spotify doesn't allow for uploading your own music, and I have some tracks that aren't on any streaming service.