IWB means "inside waist band". Most of us buy pants one size larger for IWB carry. Many IWB holsters can be worn outside the pants but support may be an issue since you will not be able to get your belt through all of your belt loops. One or more will be hidden behind the holster and cannot be used. Support is a key factor in comfortable and secure carry with any holster. IWB holsters depend on belt tightness to give good retention of the weapon against your body.
Start with a good sturdy dedicated gun belt and choose a holster after some hours of research or test fitting. I researched for a few weeks and decided to buy a CompTac M-Tac Minotaur IWB and have not regretted it since and that was three years ago or more.
Tucker Gun Leather makes nice IWB and OWB holsters as well.
Expect to pay around $80 and up for a quality holster. Custom leather is nice but will set you back a few Benjamins.
Oh, by the way, a Kahr CW9mm is a very slim small gun. I, along with many others here, carry a full size 45acp weapon IWB all the time.