OK, I created an account just to answer this for you - hope it helps.
My phone currently does what you want (I think) although it requires two button presses
I am using GO launcher and GO locker. The locker is the part you need.
With mine turned on, all I have to do is press the power button once to activate the screen and then volume down to silence (it just vibrates). if you press the up volume again it will turn the vibrate off and return the volume level to where it was and make no noise.
This locker will allow you to use PIN/Pattern (i have not used it, my wife has)
FYI - the locker is relatively new and comes out with updates frequently (they are good about that)
It also has some other nice skins you can use for it. I am using the Ice Cream Sandwich one