Roll into the Wettest Room
Account for all life circumstances and achieve maximum accessibility by planning a roll-in shower. Design a universal shower usable by anyone including the space for a potential care giver or parent assisting young children. The absolute minimum shower space, whether insert or tile, is 36 inches by 36 inches and no more than a 1/2 inch curb, beveled to provide a tiny “ramp” rather than potential tripping obstacle. Ideally, you want curb-less (flush) entry.
However for a true roll-in shower, allow no less than 36 inches by 60 inches and ideally 42 inches by 60 inches, or better still, 48 inches by 60 inches. Also plan a seat or built-in bench inside the stall. Splurge on space to make your shower the most convenient and safe for lifetime use regardless of how life happens.
Obviously install anti-slip flooring, throughout the entire bathroom but particularly in the wet area. Something you might not have considered and also the reason a curbed shower is unnecessary, the drain doesn’t have to be in the middle. Slope the floor a maximum of 1/8 inch per foot and the water can be directed to a side or corner. Linear trench, or channel, drains remove water quickly. For additional comfort, consider a low voltage, radiant heated shower floor.
As mentioned previously, block behind the whole wall on all sides with 3/4 inch plywood or comparable backing to enable custom height adjustment for grab bars or future installation of seating if you’re not already including as recommended.