For all around use, I would agree with a .22.
For ultralight concealed carry/personal defense, you may want a revolver over a semiauto pistol. Greater reliability, simplicity, no magazines, etc.
Perhaps a Smith & Wesson 342PD. From a recent review: "...the lightest of the Centennial series, weighing a feathery 10.8 ounces. Smith & Wesson has pioneered the use of titanium alloys in its revolvers, resulting in weapons that are much easier to carry concealed, without sacrificing strength. Titanium, when compared to steel, is lighter, tougher, and absolutely rust-proof. The 342PD is over four ounces lighter than the aluminum-frame/steel cylinder 442, and three-quarters of a pound lighter than the stainless steel model 640. In a pocket gun, every ounce counts, and the 342PD is the lightest concealed-hammer .38 Special revolver you can buy. Only the S&W 337PD exposed-hammer Chief’s Special is lighter, by one-tenth of an ounce."
Plus pepper spray and a knife...