I know you have to OC in a holster; however does it have to be a retention holster?
No retention is specified in the law. Only a belt or shoulder holster. Also a scabbard or case designed to carry the firearm can be used.
A lot of people swear by the Blackhawk Serpa holsters for retention, others are happy with a thumb break. I use something similar to a Safariland Stealth which is just friction retention.