Here’s a topic I created where I was helped to figure out AIWB.
Appendix is much more comfortable with a holster designed for AIWB. For example, the Muddy River Tactical Holster is good quality, I recommend it. I have used it for AIWB, but it is no where close to as comfortable as a higher end.
I recently switched to JM Custom Kydex’s 2.0 holster after being advised by @Harvey. It is really comfortable (for carrying a full size AIWB). It’s not cheap, but I was squatting at the park with my 1 year old with no problem a couple of days. It has made carrying a full-size gun very doable for me after carrying a subcompact strong side previously.
No matter what brand you get, get a wedge. You can get away with not having a wedge on smaller pistols, but with a a full size (or even compact) grip you want a wedge and a claw (some Kydex options have a wedge and claw built in). The claw and wedge help a lot with concealment and comfort.
The best names for Appendix I’ve found with my research are Tier 1 Axis or Agis and JM custom Kydex AIWB holster (they have 4 models). I’ve heard Darkstar and Keepers concealment are also good.