Thanks for all your suggestions and links. I don't think I'd make a very good job of it myself, so I doctored the photo to give a rough impression of how it might look, for the tailor's guidance. Doesn't look too bad I reckon. I've taken it back to one button, and removed the pocket flaps, which looked odd so close to the lower edge. They have a sort of stitched piping above the flap which can just be joined to the pocket opening top seam and closed off.
The back has a 9" deep double vent, which will just be shortened by half.
I could also get her to add some epaulettes with the waste material.