I’m using spectral rec.709 primaries provided by @Scott_Burns in message 39. They’re an excellent choice for this application right now because every colour in the system is treated as rec.709 and those curves take advantage of that fact to be as smooth as possible.
I believe you can achieve the same outcome with slightly more saturated primaries but once you go too far out you have to break one of the constraints:
Bounded in the range 0-1, r+g+b=1 across the spectrum, and smooth spectra (no sudden jumps or drops in intensity in any channel)