This is the one I’ve worn for years: Under Armour Mid Keyhole Sports Bra, Black (001)/Metallic Silver, Medium https://www.amazon.com/dp/B071Z8Q9YL/ref=cm_sw_r_cp_api_i_7LmhEbMBFMB9Y

It gets me just about as flat as a binder, easily flat enough to pass, and is much more comfortable. I’m about a 34B otherwise.

If you search binder alternatives you should be able to find a list of sports bras that would do this. I bought this Under Armor compression sports bra that has served me pretty well in that regard