About your measuring question, my advice is that you should measure as to how you are going to wear it. So if you're measuring at 35" waist and it's not tight enough for you, then measure yourself as tightly as you are going to wear the garment. This way you get the fit you want. I often measure below traditional waist/true waist because I don't like how little of my torso would show if my kilt went up to my ribs! How or where you measure is how and where your kilt will fit, so measure it how you want it to fit!

As for wearing the kilt at work, with your dress code and them preferring the black/dark scheme, you can possibly get away with a dark Black Watch if you want a tartan. Otherwise you could go with a solid black (traditional) kilt. I would definitely go with a PV or wool kilt. I don't think a UK Mocker is something Macy's would have in mind, but I haven't seen how it looks "dressed up".