Reviewing the criteria indicates that you want the Holy Grail of concealed carry guns! I'd like that gun too! I have spent thousands and thousands of dollars in guns, ammo, range fees, training, shipping and gunsmith fees in the quest for the gun that matches the criteria you listed.
If you don't want to read an uberpost, then just get the Glock 26 or S&W M&P 9c and be done with it.
The easiest solution is to just change your holster and get shirts one size larger. The G19 is about the best balance between capacity, size and so forth. It only goes downhill from there. It is my opinion that you do not need to change the gun. You probably just need a different holster. Get something with lots of forward cant, such as the Comp-Tac C-TAC or the DeSantis Cozy Partner.
A good gun belt is essential since it prevents the gun from flopping back. I have been using Comp-Tac's kydex reinforced belt for a year. It's very good. I also like Galco's biothane belt, but it doesn't hold the gun up as well (is fine for plastic framed guns and is too week for steel framed guns).
Is the Beretta PX4 narrow enough? If not, look at the Glock 26 or S&W M&P 9C. I find the Glock 26 to be about the best balance for a small pistol. It's very concealable with the short magazine (10+1 capacity). It's narrow enough not to print.
Why do you need a thumb safety? They're all fine and dandy until you get some pressure on you. Suddenly, that thumb safety becomes a problem. People flub them all the time. Go do some force on force and you'll see what I mean. Don't just do a few scenarios and call it good. Make sure to include some combatives where the other guy lays hands on you. OBVIOUSLY, do this with Airsoft or Simunition guns.
1) Comfortable to grip
The length of pull needs to be good for your hand. It should be comfortable with nothing cutting into your hand. Your hand should not accidentally engage the safety, slide release, or magazine release buttons.
Your finger, from the knuckle forward, should NOT touch the frame. Dragging your finger on the frame while working the trigger will mess up the shot. Grip angle is not a factor because you'll adapt to it as needed over time (which is why we practice controlled pairs, double taps, and failure drills). If you try to blame the grip angle for your bad shooting, you won't improve. The problem is the shooter, not the gun since sight alignment and trigger pull have NOTHING to do with the angle of the grip.
2) High mag capacity
Can be a problem, depending upon caliber. Increases width and length of the grip. The Glock 19 has the best ratio here. Other gun makers are catching on, so look around.
3) Thumb safety
Again, not needed unless mandated by an agency. It's actually a problem under stress. If you insist upon keeping it, then you will need to be EXTRA diligent in your practice. This means dry fire with drawing practice at least twice weekly and you better be shooting several hundred rounds a month.
4) Small enough to carry comfortably concealed
Again, this is a balance between size, ability to shoot and so on.
5) Good accuracy
Short barrels = short sight radius = harder to deal with. A good trigger is essential. In the Glock, this means using a 3.5# connector, the M&P needs APEX parts, 1911's and Hi-Powers need trigger work...and so on.
6) Rail mount
Most guns come with them, though the Glock 26 does not. Proper flashlight training is needed regardless.
7) Double action
Our ancestors knew what they were doing when they went to the double action revolver WITHOUT thumb safety. It's for fast and simple presentation to the target while under pressure. Fortunately for you, the S&W M&P has an optional thumb safety.
Furthermore, you should avoid safeties that flip up, such as on the Beretta. They're a bad design and a "CLICK!" waiting to happen after a speed reload. The other problem I have with them is that they're counterintuitive. The thumb safety on the 1911 is intuitive...it's very natural to push down with your thumb. Why handicap yourself with a goofy safety when you can have one that makes sense?
Guns I recommend you look at:
Browning Hi-Power MK 3 (will require dehorning, trigger job, magazine well bevel, night sights, and refinishing)
S&W M&P Compact (either 9x19mm or 40 S&W. Use APEX Tactical parts to get a GREAT trigger)
Springfield XD Compact (possibly too wide)
Springfield Armory EMP (
forums.1911forum.com/showthread.php?t=292373 may need tweaking)
Ruger SR-9 Compact
CZ
HK (may be too wide, but look anyway)
Glock 26, 27, 33, 36
The grip on the Hi-Power is VERY concealable because it's not that long. It's also very comfortable with Herret's grips. Throw it into a Cozy Partner and it disappears under a shirt. Magazines are expensive (only by Browning magazines). Check out Stephen Camp's site on the Hi-Power (
www.hipowersandhandguns.com). It's a great gun and you'll like it if you get it. They just need some work out of the box to make them great for concealed carry.
I do not recommend Kahr. I've had several Kahr pistols and all but one were a pain in the neck. Most were very problematic and the factory did not fix them properly. I dumped them all ASAP.
I cannot recommend KelTec either. I had a P11 and it was rough. This is a life saving tool so buy quality.
SIG is coming out with the P290. It's a single stack 9x19mm pistol. However, given SIG's track record over the past few years, I would let the SIG nuts debug the gun for you. I'd wait two years before purchasing one.
Be aware that many 1911's need tweaking to get working properly. Be prepared to spend time and money on them. They're not really a beginner's gun. Read these articles:
www.10-8performance.com/Articles.htmlFinally, there's always the revolver. The S&W "J-Frame" is probably the most carried gun in the US. These are the 5 shot revolvers with 2" barrel. Keep in mind they do require training to use effectively. You could step up to a S&W Model 10 with 2" barrel (6 shots of 38 Special +P) or go with a 686 and 2.5" barrel. However, the 686 is a bit big and you're back into Glock 19 territory.