Cheap durable (sticky) non-slip mats in the shower
My advice:
Since I did not want to use rubber suction mats as anti-slip solution for my shower and bath tub, but special stickers were too expensive for me, I decided to just go to a skateboard store and ask if you can not use those rough pads for skateboards the meter gets ... are pretty rough, self-adhesive, cheap and available in the most dazzling colors ...
It was like that. Long speech, short sense: cut to pieces, glued on, holding! A cheap and working alternative!