This package implements two specialized unit systems commonly found in cosmology. It is based on Mason Protter's NaturallyUnitful.jl, a different natural unit system that uses eV as the base unit.
For more information, read the documentation.
To generate your own conversion factors, you basically solve a linear system using something like this Mathematica code,
Solve[
{c m/s == \[HBar] (kg m^2)/
s^2 s == \[Epsilon]0 A^2 s^4 kg^-1 m^-3 ==
kb (kg m^2)/s^2 1/Kelvin == 1},
{ kg, Kelvin, s, A} ]