I'm dealing with only using one hand for washing right now (digital ulcers - can't get them wet and touching anything is excruciating), and it's challenging, but doable. I do have to note that my hair is short right now, but I don't think longer hair would be any more or less difficult. I advise you not to cut it and just aim for styles that are still attainable for you, even if it's just a low ponytail in a clip, to keep the tangles at bay. Oil is your friend, and so is satin and silk.

My other hand is starting to be affected, too, so I'm not sure how to handle washing with no hands, but I'll see what happens.