If at all possible, I talk with someone who lives with the disability I’m researching. That isn’t always feasible, so I also use medical journals, and documentation from the period about which I am writing to see how the disability in question was managed. For example, what we call PTSD nowadays was referred to as “shell shock” during the Napoleonic/ Regency era … and I was able to draw on information concerning how it was treated for Clytie’s Caller.
I researched mental health treatments for women in the 19th century extensively when I wrote In The Eye of The Beholder and In The Eye of The Storm, because one character dealt with what was called melancholia. I wanted to know how that ailment was managed. There are two characters with physical disabilities in those books as well, and I use treatments of the time to describe their situations.