Matt G had the best suggestion so far with the Para Ordnance Warthog. I can TOTALLY reccomend Para Ordnance C6LDA like I carry.http://www.para-usa.com/new/product_pistol.php?id=13
This little pistol offers the best of both worlds-1911 platform (abeit very small) in 3" barrel and slim single stack 6+1 .45acp with the lightest, smoothest DAO in existance. It does have longer reset than some other hybrid or striker fired pistols, but is a true double action only-same as an "hammerless" S&W revolver-except with trigger pull lighter than even many single action trigger pull semiautos. The very 1st time I felt the trigger pull on 1 of these, I thought the damn thing was broke it was so light/smooth! I've been professionally working on guns 27+ years, and I honestly wouldn't even try to improve on the LDA action/trigger.
If that size is still too big for you, I can absolutely reccomend the tiny little Ruger LCP .380 http://www.ruger-firearms.com/LCP/
-I carry 1 myself in my front pocket as backup to my Para .45. If you can afford it, the Rogrbaugh 9mm http://www.rohrbaughfirearms.com/
is BARELY larger than the Ruger LCP, but offers full power 9mm from basically same size package. Don't be scared off by the recall on LCPs as Kel-Tec has exactly same issues but they don't even bother to address the problem and continue to make/sell their pistols without informing consumers as Ruger is doing. Ruger has always been great about recalling even imagined issues that sometimes have never even happened.
In 9mm or .380, I would reccomend Hornady's Critical Defense ammo. In .45, go with Gold Dot or Golden saber,