You might want to consider using a compartor like the
LM339 in a custom circuit. The comparator will compare the voltage from your sensor to a voltage that you determine (using a voltage divider... just two resistors... you could even make one a pot to make it even easier for setting up) and give you a digital output when you exceed a the set voltage.
We use an OPB706A reflective IR sensor when building mini-sumo robots. It is capable of detecting the white ring around the sumo ring against the back blackground of the ring using only a couple of resistors. One to protect the IR LED from over current, the other a "high" value to tie the output of the phototransistor to ground. We measure the voltage between the high value resistor and the OPB and find that it works well in that application... but only if the sensor is within 2mm of the surface.
Jason