Grant.
I am still concerned that the warning comes on at high revs not low revs, however given your work on the oil pump, and the lack of noise from the engine, it's looking increasingly likely that the pressure switch is defective, but like you I would not want to assume that all is well. Add to that the suspicion that the switch was not in fact changed despite the old invoice I would certainly want a new one fitted before being confident in the engine.
If you can not change it yourself your only options are to trailor it or drive it to a mechanic who can. I don't know your local road conditions but if the journey can be done slowly and avoiding any hills I would be tempted to drive it. That's a risk only you can decide on.