Mental health and reasonable adjustment

I'm considered disabled for long term mental health issues. Work stress, bullying and harassment led to attempted suicide  Grievance outcome says no mistakes were made at all. OH didn't recommended anything aside from listening to me  possibly mediation and phased return, citing the cause as negative perception although there is no suggestion that my grip on reality slipped, I suppose OH can't use terms about bullying when they only have my word. My GP asked for a change of role or manager to alleviate anxiety. There are changes in the team which means other work can be available at the same pay and level. My employer refuses saying I must return  to the exact same role and manager as my grievance is not upheld. I still assert the management style of a particular manager is not safe for me. Is this failing to make a reasonable adjustment? It's a big employer with about 150 staff and lots of money. They are covering my role with a contractor and regularly have temps. My next step is tribunal but I am out of sick pay and cannot afford to quit. The union are supporting but have not been successful in getting a change in role to get me away from the same situation happening although they asked.