Where the shower drain goes decides everything
The drain is a hole in the floor, and once it's cut, the shower is whatever the drain allows for the life of the room. What it decides (the step, the seat, the controls), what to ask for, and the week it closes.
Walk-in shower or tub: which one for a body that's changing?
"I need a walk-in shower" is a product. What has to be possible on a bad day is a requirement, and it decides between a tub, a walk-in tub and a step-free shower. Plus the one decision that closes before the plumber arrives.