Do you know any good free programs to learn pullups for an overweight woman?

I'm 24 yo, 162cm tall and weight around 70kg. I progress very slowly, it took me over a year to go from 0 to 15 normal pushups for example.
I've been doing dead hangs, ring rows and negatives, my max hang time is around 60 seconds. I can do one assisted pullup with a 25kg band and that's it :( I can't do an unassisted chinup either. It feels like I'm not getting any closer to it. I know the basic exercises, but I think I need a specific program.