Hodr,
I sympathize with your position, and understand that you are truly worried. But I must tell you that you are quite simply going down the wrong road. In fact, you are just going to get yourself killed. Victor's comments were 100% correct. You will not be able to defend yourself by trying to fumble with and fire that little tiny gun. And even if you did get a shot off, if the guy weighs 200 pounds, is wearing a coat or a belt, or you strike a rib, he is going to proceed to tear you from limb to limb.
You are correct that you should only use a firearm as a very last resort to save yourself from death or immediate serious bodily injury. But, once you make the decisions to use one, it doesn't matter what size gun you use. The law treats all of them the same. So, it is really nonsensical to go with a mouse gun that will get you killed, trying to get belly close with an attacker, instead a small framed lightweight .38 special loaded with P+ rounds that will actually stop him at 10 feet and save your life.
Assuming you have your carry permit, carry it in the right hand pocket of a windbreaker, where you can easily slip your hand in and around it if you feel threatened. If you must use it, dont' try to pull it. Just shoot straight through the windbreaker.
I know it is hard, but unhook your train of thought from this tiny mousegun idea. Sad to say, but probably more than half of your assailants would be able to take it away and shove it down your throat before you can fumble it out and cock it. Don't mean to be harsh. Just trying to save your life.
Best, Mannyrock