...I'll suggest checking out the Wickers line of merino/rayon clothing at Sierra Trading Post.
An update on wool t-shirts from a merino wool "newbie".
Having lived in the far west (Eastern Sierra) for the past seven years, I'd been spoiled by being able to wear cotton in all but the winter months, so when I moved back east I bought 2 shortsleeve polypro shirts (Terrramar) which I've now worn a few times.
I started with a Wickers merino wool shirt from STP and it wasn't a good experience. They botched the order, but eventually it showed up. The seams started to separate immediately and by the time it was washed three times it looked rather seedy and had a few small holes. I didn't abuse the shirt - washed it in an HE front loader, dried it on a plastic coat hanger, etc. I couldn't detect much difference in comfort between a 'regular' polypro shirt and this merino/rayon mix. So, thinking it might be because it was about a 50/50 mix, I decided to buy a couple of 100% merino wool tees on sale at REI made by Smartwool, and have now worn them on about 8 hikes. They are of good quality, what we expect from Smartwool.
So - the question is - on the whole, did I find the merino wool more comfortable/better suited for warm weather hiking? Over all, maybe ... but it certainly wasn't clear-cut. I was especially curious about the comfort level yesterday when it was cool with low humidity and a strong breeze on the summits. After a steep pull up the Beaver Brook, and a mellow meander along the ridge before leaving the trees, nearly everyone heading down (and we met at least 30, mostly thruhikers) was wearing everything they owned, so was prepared for another layer. As it turned out, I didn't need it, but the conditions did give me an opportunity to compare whether a sweaty wool shirt would feel better than a sweaty polypro in dry air with chilly, windy conditions. Again - I didn't find the differences noticeably better.
My conclusion re: short-sleeve wool tees - there's a real 'feel-good factor' knowing that you may be helping a wool farmer in New Zealand rather than Monsanto. Sorta like putting in solar panels or buying a Prius. But, I'm not taking my shortsleeve polypro shirts to GoodWill.
As for the longsleeve tees - those will be a real test once winter comes. I got good deals on three, including a Smart wool, an Ibex and an Icebreaker.