Start with movement, not with products
Plan the clear floor area first - space to turn, space to approach the WC and basin, and space for a second person to assist if that is likely. Everything else fits around that.
Door swing is the most common problem in small bathrooms. Rehanging the door to open outwards, or changing to a sliding door, frequently unlocks a layout that otherwise does not work.
Level access and flooring
A level-access shower removes the trip hazard of a tray upstand and makes wheeled access possible. It needs the floor build-up and falls of a proper wet room.
Flooring should be slip-resistant when wet and continuous, with as few thresholds as possible. Small-format tiles or sheet vinyl with a suitable slip rating both work.
Fixings: the part that gets missed
Grab rails and shower seats are only as good as what they are screwed into. Noggins or a plywood backing layer must go in behind the boarding before tiling, at the positions the rails will occupy.
Decide rail and seat positions at design stage, with the actual user, and mark them on the wall. Retrofitting into plasterboard is not adequate.
Future-proofing without a clinical look
Even where full accessibility is not needed yet, putting plywood backing behind the shower and WC walls costs very little during a refit and makes future rails a one-hour job.
Brushed steel or matt black rails, standard sanitaryware and normal tiling deliver an accessible room that reads as an ordinary contemporary bathroom.