Undershirt

[Bman41]

This looks like it has potential.

http://www.oakeysi.com/english/products/wide-strap-cotton-undershirt.html

Or even this would work with being very hard to notice and see.  http://www.oakeysi.com/english/products/wide-strap-bamboo-yarn-bra.html

I know I know....  

But this would be perfectly unseen, do what is needed and not be to harsh and uncomfortable.

[gotgyne]

In my opinion both products are very useful if you are looking for breast support. And there are no visible bra straps and no back parts with hooks and eyes for those who might be embarrassed.
May I suggest another garment:
http://www.sassybax.com/bralette.php

John