I substituted for body rows starting almost vertical with a towel on my pull up bar. I slowly moved my feet forward through the door over time to make it harder. I then bought adjustable rings for my pull up bar and lowered until I was doing horizontal body rows. I found horizontal body rows were what really helped to do pull ups, but I would also try and do some negatives as well.
It took me a long old while to get a single pull up. Don't be disheartened, even with just substitutions and grit and determination on Level 1 I saw massive weight and body composition change, it is all well worth it. I am now on week 32 and I am in the same situation of struggling but at level 4 lol!