I've seen PEX pipe and washing machine hose used. The garden hose I used on a DIY aider was way too floppity to be useful.
If your stiffiner is rigid enough to bear your weight, it's also probably rigid enough to cut through your material. You might add some chafing gear or adjust your design to facilitate inspecting it.
I'm also playing with an idea to use two cam-lock tie-down straps as an aider, one on each foot. Footloops stay on your feet as in 2TC or knaider-swaider. Too cold to experiment with proof-of-concept at the moment but we'll see what the spring holds.