For pocket carry, Glock 36 (45ACP), Glock 43 (9mm), M&P Shield 45 or 9, or Kahr PM9.
Pants need to be loose and slightly baggy to conceal well and also make it easy to draw.
Tight jeans are not a good option for pocket carry.
38 Special, especially from the snubnose length barrels, has such low velocity the bullets do not penetrate or expand well.
Lucky Gunner has a good test write-up on 38 Special, which confirms the need to go to a 3" - 4" barrel to get the velocity up, and even then, the 9mm will provide more reliable expansion.https://www.luckygunner.com/labs/revolver-ballistics-test/
A 45 is a major step up in power which is a benefit, where capacity is limited. The Glock 36 is 7 shots of 45 ACP, which why it is my go to for pocket carry. Add a Big Dot sight up front, and it is a real defensive tool.
Boot carry is not a great option for access for most scenarios other than perhaps a backup gun.
The DeSantis Nemesis is a nice holster, but the Uncle Mike's cheap neoprene really works well too.
I made a DIY thin leather pocket holster, which I prefer as the leather causes less sweating than the synthetics.
For IWB, the options are almost limitless, thinner is easier to conceal. Glock 19 and M&P ( now go with the Compact 9 2.0) are the two dominant most obvious choices, but there are several really good options now.
IWB holsters - leather is more comfortable to me, others say the opposite.
Crossbreed Super Tuck, Comp Tac, or Milt Sparks (especially the VM2), Bullard or Davis Leather are good.
Stealth Gear, Raven, and on your On Your Six are all good quality. On Your Six is a small shop in San Antonio started by some SAPD officers.
They are less expensive, but make a nice product. Raven is really well made and a bit more refined, and a bit more expensive.
Expect to go through several holsters. Holsters in good condition are easy to sell on ebay.
Ebay is also a great place to look for holsters, sometimes at significant savings from folks trying a bunch.
A wide, very stiff belt makes a major difference in comfort. The Wilderness Instructor belt with a plastic stiffening insert is the best I've tried.
Most of the holster manufacturers also offer well made belts. A saddle shop can make something tailored to your tastes as another option.
Expect to have to experiment until settling on the right combination of pistol and holster.
Also, remember that accuracy and reliability are the most important factors, and cannot ever be compromised.
fwiw - I carry a full-size 1911 Les Baer 45 in a Crossbreed Super Tuck or a Milt Sparks VM2, and occasionally a G36 in a DIY leather holster for pocket carry.
Neither are the most popular choices, but what I have found to conceal, carry, and shoot well for me. Everyone needs to try several and work with them i.e. practice drawing and shooting, as well as carrying, to see which combination is the best all around. Anything you'll actually carry is better than "the best" that sits at home in the safe.
I went through more than ten pistols in a few years and about double that number of holsters.
The more one carries, the more comfortable it becomes. It really bothers me to walk out the door without carrying, and is very noticeable to me.
Having my gear on me is just like carrying a wallet or wearing a watch - not even noticeable now.