At Amazon you can buy the GORILLA GRIP Patented Bath Tub Shower Mat for 11.89$ on Limited Time Offer.

Feature:

• PATENTED DESIGN WITH POWERFUL SUCTION GRIP: a bathmat designed to securely stay in place; the patented mat features hundreds of suction cups that effectively help secure the mat to your tub or shower floor.
• EASY WATER DRAINAGE: hundreds of drainage holes allow for water to easily flow under the mat and towards the drain, helping to prevent water from sitting stagnant under the mat in your tub.
• TEXTURED AND BPA-FREE: the mat is constructed from BPA free materials; it features a unique hexagon design with a pebble textured topside that is soft on feet; bathmat is soft, flexible, and perfect for the whole family.