Horizon and Rainbow casinos both have poker rooms. I've never played in either but both casinos are rather low-roller but I don't know if the poker rooms are the same. I doubt you'll find anything other than low-limit games except on weekends though.

Silver Star Casino in Philadelphia, MS, also has a poker room. It is about a 90 minute drive to the east of Jackson. You may be lucky enough to find games at a bit higher limit there. I'd expect the games at all three casinos to be relatively soft.