It's perfectly legal to carry multiple firearms at any given time.
Your permit is good for as many firearms as you can safely carry on your person.
I have found that most people do infact carry multiple firearms.
Your main weapon is typically a larger caliber, (9mm, .357, .40, .45, etc), while your back up weapon is usually something smaller like a .32, .380, .38...
While that's not always the case, many people carry that way.
I'd recommend looking at revolvers, as they offer ease of use, don't jam, are typically more accurate, etc.
I'd suggest a .357, as it allows you the ability to shoot either the .357 magnum round or the lesser .38 Special round, which might be better to start with or for the lady.