If you're going R-Tech Stage 1, then the OEM Rev G will suit you fine (I did the same thing). I fitted it myself, but you could get R-Tech to do it, as they check it pre-map anyway, so it makes sense to do it then (plus I think they get it a little cheaper and don't charge extra for fitting, so that's a bonus).
If you wanted to do it yourself, then TPS or VW will supply it for around the £40 mark.
Let us know how you get on with the map.
PS - I tried the Rev D first and it wasn't that great. After a week or so, I moved to the Rev G and the car has been fine since (nearly a year on).
Either way, good luck.