I will assume you are are planning on doing the water pump AND the timing belt, and are asking what else we recommend . . .
Here are my recommendations. This is in addition to what you and @knfenimore have already mentioned
Timing belt tensioner
timing belt idler pulley
front crank seal
balance shaft seal, if the engine has one
accessory drive belts, if they’ve got any kind of miles/time on them
valve cover gasket . . . if you need to remove the valve cover during the timing belt job
If any coolant hoses look crusty, replace them now
As for the oxygen sensor, you have one, and it’s upstream of the cat. It’s undoubtedly slowed down with age, as we all do . . . but I can’t guarantee replacing it will make the car run better. It might still be doing a fine job. Have you measured its output with a multimeter?
Are the crankcase breather hoses and vacuum hoses already brittle and/or spongy?