A coherent and open reporting/responsibilities structure - one of the most soul destroying things in the office is wondering which senior person you contact, knowing there's a good chance that they wouldn't want to make a single decision if their life depended upon it and if they tried, at least four other people on the same level would chip in with different points of view. Particularly important if there is more than one wing of responsibility, such as support, marketing and technical - somebody in support might need to ask technical for a decision, but then somebody else in marketing chips in, their colleague disagrees with them as a point of pride, the technical manager wades in and has a go at the support manager and the poor bugger left with the pissed off caller watches it go all a bit game of thrones over email and still can't sort the issue, so continues to get the angry emails and calls when all they wanted was something like a paper copy of the account over the last 12 months.
A policy of automatically approving paid leave for medical appointments/treatment for all. Means people's medical conditions don't get to the point of needing time off sick and anybody who is disabled, whether or not they have declared it (as it's a significant fear for many disabled people that they will be fired/managed out/miss all opportunities as soon as somebody finds out they have a condition) will be more productive and feel less bullied when they don't have to justify why exactly they need to have another 45 minutes off work at the end of the day or take half an hour out to have a telephone consultation in private.
Recognising that disabilities are not all wheelchairs and guidedogs. Every employee should have an automatic work station assessment, rather than the person having to bring up that their chair is hurting their back and then everybody else in the office seeing the assessment and bitching about them getting a new, fancy chair.
Look at barriers to mobility without somebody having to bitch about the front door being too heavy for them to open or trying to avoid walking upstairs because the lift's been out of action for 14 months.
Proper equipment for carrying things - just because one person can carry a box of A4 under each arm, somebody else might struggle with a single ream - do they really want to have to justify why they don't want to carry 15 boxes to any random or risk doing their back in?
Ensure walkways are clear. No sticky out desks, furniture or other items. Assume a person with mobility difficulties is already working there even if there isn't.
A comfortable break area with nice, controllable lighting and seating. When you're feeling bug eyed after hours at a screen, the last thing you need is an automatic light flickering on every time you want to sit down or have to perch on a commercial reception style sofa.
Encouragement to get up and move around. No demanding certain staff are glued to their desk at all times in case something happens.
If somebody is required to stand for long periods, provide seating automatically, because the odds are that they don't actually need to stand up for 5 hours.
Breaks are non negotiable. None of the 'well, nobody else takes their break'.
Free tea, coffee, milk and sugar. No taking a 'small contribution' from everybody. The lowest paid staff might not be able to afford it and why should somebody who doesn't drink it pay towards everybody else's drinks?
A decent water cooler in every area.
Access to training for all staff. Proper training and qualifications - it's guaranteed to piss people off if middle managers have the ability to say to junior staff 'You don't need this, I need you here, not training, your job has no progression, so there's no point, you can learn on the job instead of getting the qualification, we don't need you to broaden your skills, we need you to stay here doing the same thing forever,'
Look at the dress code. Remember that running shoes and walking boots are the footwear recommended by podiatrists and physiotherapists for everybody, compared to 'office shoes'. Does it really matter if somebody is wearing trainers?
In short, try to eliminate barriers to access before anybody has to bring them up. And be open to comments from anyone who spots something, acting on them without dismissing concerns or observations or saying 'it's not been a problem before/why do you feel special treatment is in order?'