Located in London UK: Dismissed due to Physical Ability/disability then retaliated against me via firing me again citing gross negligence

Hello, I don't want to overshare just in case but I am located in London and am looking for suggestions for Lawyers who work with disabled people as a charity. I was told I was being dismissed citing my physical abilities (I have physical and mental disabilities they knew about when hiring me), they explained that it wasn't due to my disabilities but then went on to explain exactly what my disability causes (unable to run, carry heavy things, etc) again- these are things they knew about prior to hiring me. I told a parent why I was let go and they went back and complained about it to someone and it made it's way back to my ex-boss. Ex-boss then proceded to send me an email formally firing me again, this time with the reasoning of gross negligence.

I was told by some that I could sue them and win easily, but honestly I just don't want to have this stain on my record when I try to seek a new job. Any suggestions would be much appreciated.