My cat just recovered from FIPV and FIP. How long until it is safe to bring another cat home?

If it were me, I think I would wait/pass. Young kittens (under 12 months) and old cats are thought to be at highest risk. Also contagious parts are thought to hang in the environment up to several months, and some things would be hard to effectively disinfect. On the other hand, the chances of another cat catching the virus and having it mutate are small. But still, I'd feel incredibly guilty if the kitten got sick, especially since FIP is fatal more often than not. Good luck!