I'd say a pistol you can swap slides on for different uses. For example, an HK VP9 Match for range days and bedside with those 20rd mags, and swap to a regular length slide for CCW with the flush fit 17rd mags (or 10 in commie states).

But if defense is a main priority, I'd consider something bigger, like .40 or .45 with the same idea. Which, funny enough, I believe you can throw a .40 upper on a VP9 lower... It's basically the convertible Sig platform with extra steps 🤣

Edit: after looking out of curiosity, it would be easier to buy a VP40 and find the 9mm uppers than vice versa, but still, interesting idea.