Here is a link to schematics that I designed that are very simple.
Using a commercial sensor would certainly simplify matters, and I was possibly somewhat remiss in not suggesting it as an alternative.
I suppose there are many ways to do this. The approach I offered, which I thought was a simple and accessible starting point, but which could definitely stand some tweaks and improvements, is only one.
The upper part of the schematic is a circuit for a light seeking robot.
The bottom part is a reversing circuit, which kicks in when an object is in range, as detected by the IR distance sensor. The robot reverses one motor only (the other stops), so it reverses and turns at the same time.
There appears to be an error in the 'HLO comparator' section of the upper circuit.
Keep looking for a simpler circuit.