EGR cleanup, 249,000 miles. What else?

I'm sorry, I thought it was going to promt me to explain.. I got a check engine light, took it to Toyota and auto zone to read codes, spit out a p2198 or p219a, [not completely sure], bank 1.

so after watching youtube until I was blue in the face, I decided to replace upstream and downstream o2 sensors, figured I should replace/clean anything important too on a high miles prius. I want to do this right, to the point of diminishing return anyway. Plan on checking spark plugs and cleaning egr and egr cooler. What else? Do you recommend any comprehensive videos? Definitely not a mechanic..