The thing with walk in baths is that you have to sit in there in the nud while the water fills and empties which can be chilly. You also don't get right into the water, take a look at where the door ends. The air cushion kind are okay if you have good balance as they wobble when they inflate and deflate but they are a so and so to keep clean...actually most bath aids are, the water and soap and so on gets in the creases and the crannies.
Steer clear IMO of the kind that are a wide strap on a roller that makes a sort of hammock seat. As you go down and come up you have to keep shuffling sideways....notice in the ads and youtube vids, you are never actually shown the thing working. It might be worth googling to see if there is a specialist shop near you where you can go and try out various kinds of aid to see what might suit you. When i was working I tried out just about everything in the market (without water) in a professional capacity, they all have their pros and cons, they are all heavy and messy to lift in and out of the bath if you need to and they are all hard to keep clean.