The humble S&W J-Frame revolver.
This particular handgun gives you a baseline and answers the proverbial mail on the below criteria...
1- is of small & light enough stature that you can carry with various wardrobes
2- is of a sufficient caliber (38 Special -> 357 MAG) to stop a threat
3- has significant aftermarket support for things such as holsters, sights, etc
4-is of a design that's readily proven to be reliable. Run a box of 50 through it and if you can do so without issues- you're likely going to be ok.
There's plenty of other options out there but I'd argue that the J-Frame still is as relevant today as it was in decades past (heck likely even more so given bullet advancements).
-LD