If you need to take a seat in the shower, you could always build a wooden shower stool. At the link you can download the free plans to build your own stool.
A kitchen stool that will face hard use has to be strong. When you stand on the stool and hold onto its tall back for balance, you put extra strain on the joints. That is why this stool is dovetailed throughout, because dovetails make the strongest connection between wide boards. If they fit tight the mechanical interlocking alone is enough to hold boards at a rigid right angle. Adding glue is icing on the cake.