This looks great so far, it's easy to read as breathing. Im also not the most experienced at pixel art, but I'll do my best as an extra set of eyes
You might want to look into moving the torso in a less linear fashion. Maybe tip the character back a little as they breathe to create more movement.
Heres a very quick edit to explain what I mean.

That edit may be too fighting-stance-ish, if that's not what you're going for. Another thing I would suggest would be to simply slow the rising movement with each breath-

Again, I don't have too much experience with animating pixel art, so I hope these are reasonable
