Since the OP lives in St. Louis, his summers are not going to be desert like, but more like the VA summers i'm use to, hot and often pretty humid too.
Something that works well in the desert may not work well in humid heat, and vice versa. While i don't mind my poly cotton and cotton-poly blends in the summer here, they are not ideal. My Terramar Dri Release 85% poly and 15% cotton is fairly nice and surprisingly odor resistant though (nothing close to Linen or Wool though in that area).
With that said, i've found nothing so far, that keeps me as cool, comfortable, good smelling, and which is as breathable as the 100% Linen shirts, some of which i have bought at thrift stores for a few bucks, in such a variety of hot conditions.
I've tried it in the desert and in fairly hot and dry conditions, and i wear it regularly in my VA Summer humid climate as well. It's odor reducing properties are as good as wool's, if not better, and it's much more durable than wool.
Literally nothing touches it, especially an oversized, loose, button up, thin collared shirt (or also Linen pants or shorts). But like Wool, and other natural fabrics (& to a lesser extent synthetics as well), not all Linen is created equal. Cheap Linen fabric starts off a bit rough, and can be a bit abrasive at first under pack straps. Good quality linen however tends to start off noticeably softer and more comfortable. Linen also generally softens with age, no matter the initial quality. So thrift store Linen is usually a great bargain no matter what!
It dries fast for a absorbing, natural fiber (noticeably more than cotton, rayon, etc), it's natural stiffness allows it to keep off the body part of the time to evaporate moisture faster increasing the cooling effect, and at the same time it's thermally conductive to a large degree (though not quite as much as cotton because unlike cotton which are solid, flat-ribbon shaped fibers, linen are hollow tubular fibers). It has naturally high U.V. resistance and blocking also (though the latter also depends on a lot on the weave). That combination makes it the almost perfect hot weather fabric, in dry or humid heat.
What i would really like to try though, but which i can never find, is a blend of Linen and Nylon. Something around 60 to 70% Linen, to 40 to 30% Nylon ration blend theoretically should be VERY nice in the hot, humid semi south Summers here.
I have not tried so much though, using Linen as a baselayer in colder temps wherein i layer over the Linen. I think Wool, Wool-Synthetic blends, and synthetics are better for that. Linen would be much better than cotton for such baselayers, but probably not as good as before mentioned ones.
Well, i could wax poetic for much of the day on the beauty and functionality of linen, but this post is too long as it is.