Cotton works fine, it does stretch a bit when you wear it, but goes back to it's knit size when washed and dried. If you knit it in a biased/diagonal pattern, it won't stretch much at all. The chevron rib tank
could work. You may need to sign up for the site to download the pattern, but don't have to subscribe to the newsletters. If you make the largest size I think that will work for you, the ribbing helps snug it in without being too tight.