Instead of thinking of everything in terms of C, it's common for musicians to use "scale degrees" for individual notes or Roman Numerals for chords. That helps to generlize music theory without confusing the different key notes.
for example A natural minor scale degrees:
a = 1
b = 2
c = (flat) 3
d = 4
e = 5
f = (flat) 6
g = (flat) 7
A natural minor chord roman numerals:
Am = i
B dim = ii (dim)
C = III
Dm = iv
Em = v
F = VI
G = VII