I'm a T-shirt and jeans gal and it's so hard to find 100% cotton anymore. I have to admit that the spandex in jeans makes them a bit more comfortable, but I'm in no hurry to get rid of my thrice patched cotton garden jeans. Also the synthetic shirts seem to hold on to smells after washing. I thought maybe I was just going crazy but I came across a YouTube video of a lady talking about it and how to remove the odors.
I also am a novice quilter and love working with denim and men's cotton shirts. It took a few years, but I can pretty much tell by feel whether they're cotton or not and even some of the cotton ones are ridiculously thin.