We went on Iona about 6 weeks ago, we booked it just to try a 'big' ship as we are fans of little old Aurora. We had a great time, things are slightly different post covid, as they are everywhere - it's not just a P&O thing.
My preference would still be the smaller adult only Aurora but would I go on Iona again? YES I would in a heartbeat, especially during term time when there won't be many kids around.
Don't worry, enjoy your holiday and don't forget to come back and tell us how much you enjoyed it!