This thread has meandered somewhat .. the answer to the original question is found in any basic engineering text on fluid flow .. either aerodynamics or hydrodynamics ... fluid forces depend on
(a) velocity
(b) mass density
(c) a measure of size
(d) viscosity
(e) compressibility
and no other variables ....
Running through the usual dimensional analysis tricks ... these come down to the following terms ...
(a) mass density
(b) a characteristic area
(c) velocity squared
(d) Reynolds Number (Re)
(e) Mach No (M)
and no others ...
Re is important at low speeds, M is important at high speeds .. and so we tend to ignore one or the other as appropriate, and, in general, ignore Re for most CL considerations.
Re depends on density and viscosity and viscosity is roughly proportional to the square root of the temperature.
At height the end result is that the CLmax reduces .... solving for speed at the (1g) stall gives
Vs squared is proportional to 1/(CLmax x rho)... end result is that the stall speed goes up at height ..... measured as TAS if you are dealing with actual rho .. or measured as EAS if you are using standard SL rho ...... and that is the story ....