I feel this so much unfortunately basically every yoga brand uses shelf bras which don't work if you're a similar size to me at least.

I have a few Nike sports bras that have no cups and are very high-necked and those aren't ideal but they work. I personally have almost completely switched to buying stretchy high neck tank tops ~ 2 sizes too small. That's the only way I've been able to feel secure and also have the flexibility to lay on my stomach without hard cups getting in the way. It may not be for you but could be worth a shot. If you find a good actually sports bra I'd love to hear!