If you have access to a bar and long resistance bands, you can also do a variation during which you can focus on position (see this video). When my tennis elbow was bad, I would substitute HSPU for pull ups. For quantity, I would go with the bands. Quality, I would go with the wall and really focus on touching my head to the floor. For me, the band-assisted are easier. But I think a lot of it depends on your shoulder ROM.

Another variation (not for Veronica--for others!) is using something like a 36" box and getting into an "L"shape with your feet on the box and butt up in the air (see this video). This is the technique that my gym uses for HSPU beginners.

I think this is one of those exercises that people think is really hard, so they mentally block themselves to it. At least that has been my observation (at my gym).