I assume you want this primarily for self defense. Since it sounds like you are new to this so I would recommend going with a full size self loader in 1911 or a Glock 21' (SF). Get some training and experience before going to compacts or sub-compacts and make sure the handgun reasonably fits you hands.There are other decent pistols out there but these two are what I have settled on. Also you'll want to get a good belt, holster, a couple of magazine carriers, several spare magazines, lots of ammo and some training. If you think you want a revolver there are some in .45ac but I am not up to date on those.
There is more to being a good pistolero than just shooting. With training you should learn how to do malfunction clearances, the different reloads and various other things.
Good Luck on your endeavor.
I doubt you'll find a small lightweight in 45acp. Caliber alone dictates some size and weight. Probably about as small as you will find is an Officer's Model Colt or similar. Nowadays a 9mm is just about as effective and a whole lot smaller, lighter and cheaper to feed. I've tried about everything out there and I am and have been since the 1960s a 1911 man. Simplest, safest and most reliable semi I have found. Good luck in your search.
I carry a Smith m&p shield in 45 in the small of my back every day. To about 20 yards, it will hang with most of the big frames in my safe. Yes, it bites a little with handloads and 230 grain projectiles but it shoots fabulous. Just to clarify, my CC ammo is no handloads.