Debbie, often the simple things are the most difficult. A good quality and a decent fit is not an easy task in a plain item - it can’t hide flaws behind a print or extra details.
I tried Gap t-shirts because they offer petite sizing. In my experience, they pill with use. I tried Everlane t-shirts and initially was happy but they got twisted at the seams after wash (a common problem with t-shirts where jersey fabric wasn’t cut straight).
Uniqlo U t-shirts are well known for their excellent quality. I cut hems in some t-shirts and wear longer ones under sweaters.