To me, although effective, this up and down approach seems a bit outdated. Perhaps it’s simply the best solution though, in the example you provided it definitely makes sense.

Tenshi: Yes, but jump won’t be really used that much.
Until today it was like you described it. I changed so you can choose to go up or down.

You could just let the player hold the “shift” key pressed when he wants to walk up/down on stair-tiles. When no shift is pressed, he just walks through the stairs, except if he is already standing on a stair tile, in that case he doesnt fall through it.
I think it’d be a easy-to-learn-hard-to-master combination that would be very advantageous to expert players.

In the video, the stairs going down begin about a meter behind the stairs going up. So the advanced, quick-reflexed player who wants to go down the stairs would press shift right after passing the stairs that go up. *hopefully understandable*