FastLED.h
and
Adafruit_NeoPixel.h
can both be used at that kind of minimum level.
They both have other stuff which may take up memory.
They are both open source, so.
You might like APA type smart LEDs that work on a data and clock basis, you can do without any library whatsoever and you will indeed be on your hands and knees free of anyone else's ideas about how to make things "easy".
HTH
a7