Whoops, missed that bit.
Try going through Luxire, and just making small alterations to a shirt you already have. I had good success at the start with just making a small shirt fit everywhere then changing the neck measurement to fit how I wanted, as this is my main problem with RTW shirts.
This is pretty much what i did, just took measurements off of an existing shirt. Since the construction of a shirt is fairly straightforward, the resulting fit should be very close.
From there you can start playing around with subsequent shirts, and matching fit to shirt style.
I went through Elite, but that was before i knew of Luxire. Luxire's shirt construction and detailing is pretty fantastic, they use nice buttons, and you can go nuts with specs like shirring, placket design, and collar dimensions. Elite's not bad either, my shirt fits very well and has a good collar, but Luxire strikes me as more of a specialist. For the money it's very impressive, and fit is king, but the cloth is obvioulsy going to be the weak point (it's not bad, but it's not great).