There are some pretty good responses here to your original query. You are looking for something that has easy concealability and can be large but you want to be comfortable. Let me start off by saying I too am a new shooter and carrier of a firearm. I did around 8 months or so of really serious research before I made my final selection. That research led me in many different directions from just owning a firearm to accessories for the gun to re-loading to prepping for survival, etc. Pretty intense stuff. Here are some of the things I learned about buying a weapon for concealment carry. I am going to focus primarily on semi-automatic handguns and not on revolvers.
A person can carry just about any size weapon comfortably except for some of the heavy hand-cannons. Concealing it is another story altogether. The length of the barrel isn't the problem when trying to conceal. It's the grip that sticks out and says to anyone observant enough to notice, "Hey, there is a gun under this shirt." Now, it's a fact that most people, at least here in the US, do not observe other people very closely. Especially close enough to see the printing of the grip. But, some do.
So, the full size weapons are great with standard barrel length which aids very much in accuracy and usually an increase in rounds carried in the magazine. The smaller the pistol, the less barrel length, therefore accuracy, and the less rounds in the magazine. But, they make excellent backup guns.
However, most pistol manufacturers have come up with what I think is a decent compromise. The compact pistol. The compact pistol usually has a slightly shorter barrel and a smaller magazine, but it has the capability of adding one of the same models larger magazines. Some manufacturers even have sleeve extensions for those larger magazines so that when you insert it it gives you the exact same number of rounds that the larger model does and it feels just like you have the full size in your hand. Two excellent examples of this are the Ruger SR9/.40C and the Springfield XD(m)9/.40 Compact.
One of the suggestions made by earlier response to your post was to go to a gun store or a gun show and check out the different handguns they have. Pick them up and hold them. Get a feel for how each weapon grips in your hand. How is it balanced? Does it feel good there? Does it feel uncomfortable? There are alot of Glock fans that have posted responses. The Glock is, by reputation, an excellent weapons platform. But, for me and my big hands, those little finger grooves just don't fit comfortably in my hand. Also, if you can, shoot a few different choices on the range. Some of the gun stores have gun ranges and can rent quite a wide variety of guns. This will give you an idea about how the recoil of each gun will affect you and what it sounds like when firing it.
Something else to consider is calibers. Everyone has an opinion about what the best caliber is. In my research, I found that the general rule of thumb is, for a primary weapon, it shouldn't be less than a 9mm. So, the four choices left are 9mm, .40, .45, and 10mm (even though this is less common than the other three). Most people go for the .40 or .45 because, "if you can handle the recoil, more is better." For me, 9mm is much cheaper to shoot and in my opinion, if you learn to shoot as accurately as you can and you put 9mm rounds center mass of an assailant or in their head, they will go down. I just bought a 9mm, but I hope to widen my options at some point by getting something in both the .40 and the .45 in the future. In other words, don't get stuck on caliber too much. They will ALL work in a critical situation as long as you take the time to grip and aim your weapon of choice properly.
I did alot of research by getting into forums like this and just reading what everyone had to say. I also went to youtube and checked out some of the gun community there and watched some truly awesome reviews. Hickock45, nutnfancy, sootch00, humans4targets2, fateofdestiny, sturmgewehre, and a host of others have more gun reviews than you can imagine.
Here are a few guns that I considered for conceal carry:
Ruger SR9C (this is what I chose as my first handgun)
Ruger SR40C
Springfield XD9SC (SC=sub-compact)
Springfield XD40SC
Springfield XD(m)9 Compact (my second choice)
Springfield XD(m).40 Compact
Kimber Compact II .45
Kimber Pro Carry II .45
Glock 26 9mm
Glock 27 .40
Other gun manufacturers who are more expensive (which is why I didn't research their guns further)include Walther, H&K, Beretta, etc. Some folks like Taurus. I don't particularly care for them for no real reason. Read about different issues with different guns and dropped from my consideration list I guess. I picked up a Hi Point in a pawn shop and racked the slide back. It jammed in that position. DO NOT GET A Hi Point.
For smaller backup type guns (all 9mm with 7+1):
Ruger LC9
Kel-tec PF9
Kahr PM9
Kahr CM9
Kahr CW9
Beretta Nano (just heard about this, so I don't know much about it)
Kimber Solo (I heard this one has problems dropping the magazine out when shooting)
One more thing to consider is holsters. If you are going to carry concealed, even if you are just carrying a pocket gun, you have to have a holster. You can get an IWB (inside waistband) or an OWB (outside waistband). If you live in an area where you can wear jackets or light button up shirts out, then maybe an OWB would be good. I live in the Great State of Texas and man does it get hot here. Too hot really to wear a jacket and I can't wear a button up shirt (either unbuttoned or buttoned) loose at work so for me, that means an IWB. Do the research, there are many great manufacturers out there for this. The Springfield line comes with a holster, but I would recommend that if you chose this, to wear it only until you get the one you ordered. There is a youtube video where two guys do a demo showing how easy it would be for a bad guy to walk up behind you and with a quick twisting motion get it and your gun away from you. Not good at all.
Some holster brands:
Crossbreed Supertucks
Texas Tucker
Serpa
Blackhawk
DeSantis
Tip: If you buy a new gun. After cleaning the shipping gunk out of it, go shoot no less than 200 rds of FMJ (full metal jacket) or more and at least 50 rds of whatever self-defense ammo you are going to use. This "breaks-in" in the gun and helps you insure that it will dependably fire those particular brands.
Last, but certainly not least:
4 Basic Safety Rules to adhere to at ALL times:
1. Treat the gun as if it is ALWAYS loaded
2. Do NOT allow the muzzle to point at or "sweep" anything or anybody that you are not willing to destroy
3. Keep your finger OFF the trigger until you have the target in your sights and are ready to destroy it.
4. Know your target and what is behind it, in front of it, and beside it before you squeeze the trigger.
Remember, research is key. These are just some of the things I have found out. You really should go and find these things yourself. You will be surprised at some of the things you learn along the way. Good luck and good shooting.