I'm running what I call Dungeons and Cthulhus set in a Planescape setting. I use the SAN rules from the d20 CoC with slight modifications, which are:
The sanity rules from Call of Cthuhlu are used with the following changes.
For most creatures that are not pseudo-natural, a sanity check is not required unless the character believes the creature is of immediately hostile intent. Pseudo-natural creatures cause SAN checks just by lookin' at 'em. They're from Away.
Psychoanalysis is a class skill of clerics, seers, telepaths and monks – though they do it rather more mystically than modern psychologists. Certainly some spells and powers will also help a person in terms of SAN – nevertheless, SAN can't be raised to above the character's Wis x 5 except through adventuring (overcoming various horrors and all).
A creature that has a SAN check rating that has the pseudo-natural template added has the amount of sanity lost from seeing it increased by two die steps. A d12 becomes 2d8. A d20 SAN loss becomes 4d8.
Only pseudo-natural creatures and evil outsiders – meaning those with the pseudo-natural template or from the Far Realms – cause moral corruption.
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These are my notes and make sense to me. If you have trouble with 'em, let me know and I'll aim at clarification.
I am also handling actual insanity differently, in a way not discussed above. Instead of having the players be forced to RP various mental disorders, I have a huge list of the sort of halluncinatory things players might see. When they're crazy, I start throwing them in the game so they don't know what's real and what's not. So far, so good, and my players are willing to RP out the various insanities, too.
And, remember, Conan was a Mythos character! What you're thinking of doing is pretty normal.
