I have some t-shirts from Ably that I've had success with -- they are treated cotton. I have tried merino wool of various brands but I have a long trunk and so a bit hard to fit and most of the merino t-shirts I've bought are too short. The key as the OP says is to give them a rest between wearings. I usually will rinse them in the shower or sink wash (or use my Scrubba if I brought it) after 3-4 wearings.
I always bring a fresh set of everything to wear on the flight home. A couple times that has come in handy when I've had a "gastro emergency"
