Please help with ab workouts and six pack?

I’m a teen female and I am looking to get a six pack. I am involved in a crew team in which we run 1 mile everyday, do many ab/core workouts, run up and down stairs and of course, do the rowing machine. I was wondering if I should buy an ab lounge or just get the attachment for my perfect pullup bar where i can place my arms in the hanging strap things. It KILLS me to do situps and crunches on the floor (my back). So ab lounge or the straps for my perfect pullup bar? Thanks so much!
yeah I made an ab ball by filling a basketball with sand and duct taping the whole thing.

My lower back like right above my butt always curls up so I have an arch when I am doing some things with the ab ball. I hold the ball with my arms all the way extended behind my head and lift my legs up. The ball is like 15 pounds and I am 130. Is the ball too heavy? i dont know…