How to stop your chest from bouncing while running or doing jumping jacks?

I know the obvious answer is a sports bra, but I have tried on sports bra after sports bra, & nothing seems to give me the support I need. I'm unfortunately a DD, so finding my size is already hard enough, & if I bounce when I work out, it REALLY hurts. I can't just stop doing jumping jacks or jogging because I'm working with a personal trainer, & I have to do what he says. I would also feel stupid telling him a can't do something just because of the size of my chest. Does anyone have any advice for how to stop the bouncing?
How to stop your chest from bouncing while running or doing jumping jacks?
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