+1 to everything that has already been posted here, but I want to add one more tip:
The achievement is for REACHING the Gorog without hitting any debris. That means if you have already reached him and attacked him, are falling through debris again and HAVEN'T gotten the achievement, you won't get it and need to start again. This will pop the first time you catch up to him, assuming you avoided all collisions. I did this fight three times before that occurred to me and wasted a lot of time doing so.
The suggestion by Protium regarding the costume change WORKS, so if you even think for 1/10th of a second that you might have hit something, change your costume and start again. It's worth the extra ~15 seconds to not have to go through the whole boss fight again.
One last thing: you can get this achievement and "Use the Force, Luke" at the same time. Start the boss fight and never touch the X button, except during QTEs. If you mess up and accidentally use your sabers, you have to start the whole mess over again (sorry!). Assuming all goes according to plan, Stay on Target will pop when you first catch up to the Gorog during the fall and Use the Force, Luke will pop at the beginning of the cutscene.
Good luck!