MMBD4148SE would be a good general purpose diode, you could also put a 5.5v varistor between the IO on the pic and the gate on the FET if you wanted maximum protection, although I think it's generally not needed. In my opinion if you were to put an over-voltage device on the circuit the Varistor would work better because it acts faster than a zener. Any reasonable package (assuming surface mount)...like 0805 would work.

Incidentally, I was looking at your requirement to not draw more current thru the regulator and in my mind this low-side drive would ensure you are not sourcing thru your power supply for the pic. I am assuming this is an external relay or something you don't want mixing in with your signals on the board.

This particular circuit i have suggested has been tested to well beyond 1Million cycles on a bench. we finally decided we'd beat it to death and took it off the supply during testing. This circuit would also appear to reduce or at least simplify your drive circuit design. BJTs are cool, but the FET is a bit less mysterious for driving a circuit like this.