For basics, I'm actually a huge fan of Daily Ritual, which is an Amazon clothing brand. This shirt is like my top ten of all time. It's amazingly soft, stretchy, and has a great shape to it that manages to make it apparent you have TWO breasts (and not just the singular chest-chunk you get with a too-tight shirt) AND a waist while also not clinging to all the little pooches you'd rather not showcase. Super flattering, although I do recommend going with a size up from whatever your old navy size is.
Their tops and things tend to run for about $10-18 apiece if that's something that fits in your budget. They also offer free returns, but that may be a prime-exclusive benefit (I am also 100% willing to stick you on my prime account if it would help you, just message me).