I don't have any experience in this matter, but I do have a thought.
It seems to me that one has to sit (naked) in the tub and then fill it with water, and then after bathing, remain in the tub naked while it drains. I think I would be chilled if I had to do that.
A walk in shower with a nice sturdy bench and hand rails seems like a better option. I think it might be esthetically nicer as well...particularly if the home is sold in the future.
I have no idea of the cost involved in these two options or what your budget will allow, but I hope you find the perfect solution.