I used to play this and "Within a Deep Forest" all the time when I was in college. It was really comforting and relaxing, and I still have the soundtracks of these games to this day, and "Confiant" from Knytt Stories remains my favorite song.
Unfortunately I haven't played KS for a long time, so I can't immediately suggest some good levels. The level archive is a mess so it will take a while and a lot of trail and error to find the good stuff.
Speaking of games with level editors: Dustforce has become my go to quick chill game. Despite how difficult and demanding it is, the atmosphere of the game is always calm, and it's really pleasant to play and replay stages. Stressful stages like "Hideout" are disarmed by the atmosphere set by the music and quick restarting. It's really a nice game to have.