I use a Bose QC 25, (note 25, not 15), with a UFlyMike.
I found you can easily wear the headphones backwards, which puts the mic (and cable) on the right hand side for an F/O.
Make sure you measure accurately the length of mic boom required when you are ordering. Slightly too long is better than too short, (ooer missus!), since you can bend the gooseneck to put the mic against your lip.
If the battery runs out, the QC25 headphones and mic all still work. You lose the active noise cancelling, but having full ear cups, you still have some passive noise reduction.
The QC25 is a very good and very comfortable noise cancelling unit, if you can find a set.
I think UFlyMike produce a mic for the QC35 now?
The combination is a hell of a lot cheaper than the A20, and the A20 is also very bulky and heavy by comparison.
PS, you have to pay duty when importing the UFlyMike, which being an American company, they don’t know about so they can’t tell you. And it costs more than the headset. However, it is a very well engineered and well produced product, and the after sales service is excellent. I fully recommend them.