For the Beretta Nano:
Weight is fine if using a good belt. No belt and the weight will annoy you.
Use a kydex "skeleton" holster* in order to cover the trigger and to eliminate the bulk of a standard pocket holster. There's no safety on the Nano so I wouldn't recommend carrying it without a holster of some kind if there's one in the chamber.
For a one-handed draw and fire, the kydex holster can be tethered to a lanyard. The other end of the lanyard loops around your belt. When pulling the gun from the pocket (with the trigger finger placed on the frame above the trigger guard for safety) the lanyard's slack is taken-up and the holster is pulled free of the gun.
*Pocket Rocket pocket holster from Statureman:
The holster covers the trigger and is held firmly in place by wrapping around the slide as well. Great price and service—highly recommended.