Very nice OP. Strange that few cyclist use mirrors. Last year I bought one of the third eye set-ups that clamp to your glasses. I used it a couple times but found it to be too much of a distraction while doing my sight-seeing trips. That's the main issue with head mirrors. Nice to have when needed but a real distraction if you're not used to using them
I've thought about a bar end mirror but one of those would interfere with my hand position while climbing. Now one of those might work if I can find one that has an extension and is not too big.
For the most part I don't think you need a mirror unless you make a lot of lefts into heavy traffic. Personally I don't so unless that changes real soon I wont' be too worried about it. I just turn my head to check traffic when needed and at least for the time being this seems to work.