I really like the Seecamp .32 ACP. There is a same-sized .25 ACP version, but .25 ACP terminal ballistics are so anemic that the .25 ACP is a non-starter. There is also a slightly larger and heavier .380 ACP version.
PRO
• really small
• really lightweight
• so flat that it never prints in even the lightest summer clothing
• heavy enough trigger pull that pocket-carry does not require a holster
• not a rimfire
CON
• only feeds hollow-points, so cannot use the Buffalo Bore 72gn +P hard cast lead or inexpensive FMJ practice ammo
• has a really annoying magazine safety, so the slide cannot be racked or the chamber emptied unless the magazine is in
• heel magazine release
• "only" 6+1 capacity
• not a 9mm or 10mm :-)
The North American Arms Guardian is a close copy, almost as small and lightweight, has a standard magazine release, does not have the magazine safety, so is more easily emptied, and does feed +P and FMJ rounds. Largely because the NAA's manual-of-arms is simpler and more consistent with her other pistols, I bought one for our daughter to carry completely inconspicuously at work.
Because of my COVID-related hearing loss, I gave some thought to having a custom threaded barrel made for either the Seecamp or the Guardian, but decided one of our Glock 43's with a Gemtech Aurora II can was a better option at that form factor, though still not practical for on-body carry.