In reply to GrendeI:
I have recently got some merino boxers from a fairly new company called Armadillo. Long in the leg and they have a fly. I am a 34 inch waist and the large fit me perfectly.
I got them half price from Sports Pursuit. Full price is £40, which is about normal for merino.
It is too soon to comment on durability, but they are aimed at squaddies as an alternative to synthetic base layers, so that may count for something.
Rich