What can I safely use to reduce redness and itching from allergies if I've had cataract surgery?

If your cataract surgery was more than a month ago you can use anything any other person would use. Moisturizing and lubricating tear supplements can be purchased over the counter and are good for mild conditions like you have described. More resistant cases might benefit from Naphcon A, or Opcon A, or other over- the-counter medications. These should not be used for more than a week or two. More persistent symptoms as you have described are best evaluated and treated by an ophthalmologist as they can be more troublesome than dry eye and seasonal allergy.