IMO, you should look for a retention holster. If it has to be closed-end, I'd recommend a Federal holster, though for most other cases I personally prefer the counterpart Uncle Mike's holster. Both are inexpensive, but they'll do the job unquestionably. You can also look for a rig with a thigh strap; that'll keep the holster from flopping about when you run.
As far as chambering it, yes, I would keep one in the pipe with the safety on. No, you never trust a mechanical device; that's why you strictly adhere to the 4 rules. Number 3 is of special importance here; keep your finger OFF the trigger until your target is sighted and you wish to fire at it. If you obey the four rules unwaveringly, you can keep that gun cocked with the safety off and it won't ND.