You can do it solo. I did it solo with no problems at all. First off the Bandana Skull (infinite ammo) helps so much with pretty much every achievement, so get that if you haven't already. However this is not needed at all to get the achievement. So
all you need to do is every time you get a checkpoint, save and quit. Then reload your game, and repeat at EVERY checkpoint. If you do happen to die, simply hit the guide button and return to dashboard. Load the game again and repeat if necessary. If you
die... DO NOT hit start then revert to checkpoint. That voids the achievement. I died one time in the middle of the level on my solo run and did the technique I described above, and got the achievement. You got this!