L.M.
I don't know if this will help, but you may want to try www.onestepahead.com they have all sorts of gates. Maybe they will have something that will work for you. I know they have a soft gate, maybe you could rig it up to work for you? When my guy was first mobile, I just used a dining room chair in front of the stairs. It only worked for so long, but it's a suggestion. It depends on how mobile he is.
Good luck!