these at 1 or 2 a month. Might not work for you due to your cotton criterion, however they are brilliantly comfortable; I doubt I'll go back to cotton.
I prefer V or U front t-shirts pretty much year around as they do not show when one's collar is open, and wick moisture away from one's body in hot weather.
If in doubt - overdress.
"His modest resources meant that he could dress no more than reasonably well, but he did so with a kind of faded elegance that ignored the dictates of fashion... the overall effect was of someone frozen in time, indifferent to the new fashions of the agitated age he was living through. The truth is that he took pleasure in this, for obscure reasons that perhaps even he could not have explained."
You can find them new and used on ebay as well.
No undershirt here---ever. I got tired of wearing them when I was eight and haven't worn one since. Then again, I don't sweat much at all. It has to be blazing hot for me to sweat so it works out fine for me.
I never wear really thin dress shirts anyway so you can't see through them and a t-shirt just feels too confining to me.
People think they are so rebellious and original, when really they are just banal, boring and dumb.
I always wear an undershirt. In South Florida, it's typically over 85 year-round. The cotton undershirt keeps my dress shirt from sticking to my sweaty (although handsome) body. Avoids embarrassing underarm stains, too. In my opinion, there's nothing more distasteful than seeing a man's sweaty, hairy chest through his dress shirt.