Do the bra underwires poke or pinch the chest in the front ? Before you start bending them or you throw the bra away, try this:
sew a dart in the bottom part of the center of the bra. A dart looks like *this*, to make one you fold the bra in the center and sew like *this*. The dart should be 1 cm wide in total (that means: sew 5mm from the fold).
The "bridge" of the bra pinches due to the construction of the center of the bra. It is not the fault of the shape or size or elasticity of the underwires.
The darts don´t look pretty, but make a huge difference in comfort. If the material is too thick, the dart may be too big, and will press itself uncomfortably into the skin. If you´re more skilled in sewing, try cutting open the tunnel of the dart, and sewing it flat.
Thanks to effuniak for this fantastic tip !