Whoa!! First song I encounter on this forum that's not overcompressed or overlimited. Congratulations!
It could use a bit more high frequencies, yes, a gentle high shelf filter starting @ 5 kHz could do the trick.
I was impressed with the stereo width.
Tbh, I don't know if the drums should be raised in volume, I think it suits the 'gentleness' of the song.
EDIT: I opened the song in my daw and I see that the song is limited at - 6 dBFS. So it's possible to turn the song up by 6 dB without addition limiting. The loudest parts gave me 10 dB RMS and no distortion. Nicely mixed!