An airweight or Ti snubbie may be an option, but you wouldn't really save any space that way. A .380 Guardian might fit the bill, but those are a bear to shoot, from what I hear.
Here's a quick rundown of the current .32 "mouse guns" which fit your listed requirements...these are the ones I've owned and carried, at least.
Beretta Tomcat (.32 ACP):
Feels like a bigger pistol to hold and shoot, good sights for a mousegun, pop-up barrel is a great feature. Early models had quality control problems, but later models generally work very well. I've owned two, and both have been trouble-free. Avoid dry-firing without snap caps, the firing pin will break for sure. A bit wide in the grip and rather portly in size for a .32, but those attributes make it shoot like a big gun.
Kel-Tec P32 (.32 ACP):
Incredibly flat and light, very pleasant to shoot thanks to the locked breech. Not a very ergonomic gun, folks with big hands usually find the P32 a bit difficult to hold and shoot well. Sights are rudimentary, and the overall look and finish is a bit homely.
NAA Guardian (.32 ACP or .380ACP)
Jewel-like quality, a very compact pistol, but a bit on the heavy side thanks to all-stainless construction. Straight blowback like the Tomcat, but a lot less pleasant to shoot thanks to the very compact grip. Long and hard DAO trigger, and very tiny sights.
After owning and toting all of the above, my current mouse gun is a Beretta Jetfire Stainless in .25 ACP. It's shorter than the P32, lighter than the Guardian and the Tomcat, and comes with the handy tip-up barrel.