is the QRB1114 still a valid part ?
from a mm away, nail polish will be 'reflective enough' to get a strong signal.
white paper and black paper, white out.... whatever.
any combination of send receive should work. if you hve an old ball mouse, there is an optical interrupter that could work if you can cut it in half and install side by side.
to test, you could try a light sensor and an LED and see how much light is reflected.