One post is PLENTY, my friend. You will be unable to decide this issue until you perhaps get some cardboard, create a tray, plastic drop cloths for "glass" , also cardboard for walls , and go stand in a makeshift you create.
What someone ELSE thinks is large enough, may be too large. Much of the way a shower looks and feels has to do with how closed it is. The more glass? The larger it FEELS. 48 x 60 with ONE wall of glass, will feel smaller by far, than one with two, or three walls of glass. Not one interior inch will change, only how it feels, including the light you may enjoy.. You are reinventing a wheel,.
Bear in mind you do not spend the entire day in there : ) I can assure you, a 48 x 60 shower is extremely generous for getting clean very comfortably, no matter the wall material or amount of glass. Two can fit as well. Remember you have to clean it, unless you hire that out. These folks do. It's 4 x5 ,4 x 6 , 4 x5 respectively in pics.
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wall ideas
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