Unless you are in the habit of wearing tight form fitting tops there is nothing to fret over. Plus your general build can help a lot in the disguising department.
For instance, I have never worn form fitting tops, even a tee shirt. About the closest I get is a undershirt. For work I wear dress shirts. Plain, not tailored, fitted or what have you. Loose and baggy. Which I guess is normal for guys shirts. It is not like I have a big neck, just longish arms. Tee shirts are always bigish and floppy. A throwback to being a long time fatty. In male mode I still abhor tight clothes. In my much slimmed down size 8-10 fem body, tighter clothes tend to rule.
I have a good full A to maybe a B cup depending on the bra. (yes, like most womens clothes there is no 'Standard'. I can fill out a size 8 dress or a size 12) Without a bra my boobs are pretty much unnoticeable. Even by me. The only time I get a hint of them is wearing a seatbelt when the strap lays tight between my mini mounds.
When I wear one of my favorite Wonderbras, well they are hard to miss