I like the 45 (it is now the only handgun caliber I carry) but my compact Kimber Ultra does have a decent kick - enough that my wife really doesn't like to shoot with it.

Best go to a local range that also lets you hire out pistols and try a few sizes and calibers.

As regards caliber, people will argue furiously and at great length about shot placement versus stopping power so anything I say here will be hotly contested. In reality, there are no right or wrong answers - only what suits you.

I would take a look at 9mm polymers.