Hi! I know this isn’t exactly what you asked but there is a way to add external music to bitsy, so if you found some public domain/creative commons soundtracks you liked you could add them with the “bitsymuse” hack on Borksy? (Google borksy and then tick the Bitsymuse hack, edit the code so you have the names and filepaths of the songs in a zip folder next to the rooms it gives you).
As another non musician making bitsy games, I don’t really have a lot of tone recognition, so I try and go for visual patterns instead? Music seemes to like staying close for the base, try only going up one and returning to the original. C is usually a good note to loop around. The main notes like going up/down in a staircase pattern, or repeating/mirrored patterns. I have no idea if any of this helps or makes sense but here you go!
Also bitsy has a function to copy and then slow your song, or put it in a minor key, so once you’ve made a song you feel ok about you can make variations very easily to shift the game tone!