You want something like this: https://www.fringesport.com/collections/strength-bands/products/latex-free-strength-bands
Doesn't the matter what brand that's just the first thing I came across to try and find a product for it. Nice and wide so it can sit comfortably and provide a decent amount of resistance. Double them up if you need more help.
One way to get started without the bands is to just jump up as high as you can and try to grab onto the bars at your highest point, then try to lower yourself back to the ground as slowly as possible.