Consider a separate curbless shower to keep the water out where it shouldn't be.

There are a number of considerations if this is going to be in a renovation. What is the depth of the existing floor framing deck ? What is the direction of the joists; what are the spans of the existing joists ? Where is the drain and do you have enough run if you move it ? Once you have a grasp on the practical constraints, given your condition I would go curbless in the shower, ensuring wheelchair access at all openings. Not sure you need to go all the way to a wet room, but rather an open floor and shower plan, with adequate sized and pitched drain. I do not know your climate but here in CT, heated floors and shower walls are a nice luxury to help combat the open nature of the shower. I would not use a low level shower base - definitely curbless. Hope this helps.

Thanks for the feedback on wet rooms. Again, one of you says shower base the other not. The bathroom floor is concrete, so I have no problems with joists. I am in the UK, so heating is a must. Also, I have never seen a "curbed" base, but would this not ruin the overall looks of a tiled bathroom?
Thanks all.

Concrete floors are better for wet rooms, factors to think about first are drainage and getting the fall of the floor right for the drain, you may find you will have to break up the existing floor which will get more costly. Get plenty of estimates and references you don't want damp coming through the other walls, and get the layout of the room you want.

I cannot speak to the UK. In the US it is very common to have a 4 inch curb built up in front of the shower to keep the water in the shower. As per my previous posting, for your application I do not believe that is what you want. Further, I suggested to go with a "wet shower" not a whole wet room because of likely physical constraints. As mentioned above you need pitch for drainage and you will need heat to keep the space comfortable. Concrete is an excellent base but as noted you may have to hammer it all out to get the pitch, move the drains pipes, add radiant heat, etc.