Have you checked the seatmap to see what's available?

Haven't flown the A359 yet but reviews make it seem row 30 or combining row 40 BC with Row 41 A, would be a solid set of options (and then see if you have recourse to have a refund on the C+ cost), and likely worth keeping the original itinerary.

https://blog.wandr.me/2017/11/where-...50-best-seats/

I would go into the conversation tomorrow with some options in mind rather than letting the CSR dictate the conversation and provide the options.