A big master bath is best for ample maneuverability including family members who use mobility equipment. If possible, a second entrance accessible to all family members and guests increases the flexibility of the bathroom. One easy renovation is to convert to an out-swing door to eliminate accessibility issues in and out of the bathroom. Another more ambitious idea is to position two sinks at different heights to accommodate all family members: kids, adults and especially aging adults. The lower sink can also accommodate a seated user. A large curbless shower works for everyone in the house including pets and plants. Putting wood blocking between the walls in showers and around toilets, before installing drywall and tile, adds the foundation for support bars.
If your current bathroom footprint is small, prepare to make modifications to adjacent rooms as well to gain the extra square footage. Multiple floor drains are best, and the installation in combination with a gently-sloped floor is expensive and intensive.
There are many advanced floor systems that make the installation of an attractive, leak-proof, curbless shower floor much easier.