I match the gun and cartridge for the intended task they will be used for, not my own comfort level or ability.
With your limitations, I'd be looking at a 12 ga. pump or maybe a .44Mag, or .45Colt in a lever action carbine.
All I know about bears is from watching them on National Geographic TV shows.
But if I was going to shoot one with a .357, I'd want the biggest, badest load that wouldn't blow the gun apart to do it with.