Unfortunately having a railway network built largely long before such issues were considered, having uniform door levels will not alleviate the disparity of platform heights, curves and cambers.
A much simpler answer is to ensure that whenever assistance is booked & needed, that crews / station staff are aware & reminded at an appropriate time (i.e. on approach to the start & destination stations) that they have passengers that require their attention.
But that does not meet the requirements of the Equality Act.
If you have a turn up and go service for the abled then you have to have an equal service for PRM, not one that requires special and specific booking arrangements. That’s why changes to infrastructure and rolling stock are the answer to the problem. As mentioned above, technology exists allowing step free access arrangements in other countries already, time the UK took the requirements more seriously.