I got me two of those fancy workouty tanks with built-in bras from Forever 21 when I realized a body-hugging cotton tank was not cutting it anymore. They’re fine. I think tightness is key, for aforementioned down-dog reasons.
I pair these with small pajama drawstringed shorts of unknown provenance. They’re also fine.
The only activewear I take semi-seriously is swimsuits, anyway.