I don't know if you can see from this picture, but I put in a plastic (flexible) folding door.
I added the board and track across the top of the opening and hung the door.
I cut it to length to have it drip inside the shower pan.
I can't tell you how well it works since we haven't used it yet.
Here is the link to the Lowe's listing. It is made from PVC and can be cut to size fairly easily.
The closure is a magnetic latch and has handles on each side.
Not fancy, but probably adequate and
light.