I think if no one would help me adapt my house, I'd try to get help with adapting myself to my house? Are you in mental health therapy to help see if you can work to get better/sooner?

The "experts" can't tell you when you will get better because it's an individual thing, dependent on you. I would set goals on working to get better and/or adapt my downstairs to help me, etc. but with the expectation that you'd be able to get upstairs and down in X period of time and working toward that as a goal.

Is there no one in your late partner's family that "should" be in the home? I don't know why you would hang onto a building that isn't helping you, is making things harder for you. Could you maybe rent out the place for awhile and fine a better flat for taking care of yourself and working on getting well? Maybe it's the circumstances of the house that are helping hold you "in place" instead of allowing you to move freely about your life.