kestrell | Fabric question

I'm trying to find a brand of white 100 percent cotton t-shirts suitable for dying. My default is some variety of Hanes heavyweight or "beefy" t-shirt. What I don't like is the t-shirt material that feels stretchy and thin. I'm also confused as to what terms like ring-spun mean, along with the 5 or 6 number which seems to refer to weight.

Any recommendations/explanations would be welcome, thanks!