I struggled with this too, not the stairs, the backache. I went through a few variations of options, I eventually made a lap mount for my x52. Its basically a glorified bit of 18mm ply with the hotas bolted to it shoulder width apart, as I sit on the sofa and play. I can post a pic if you're interested.
The x52 is definitely not designed ergonomically to be used at normal desk height, imho.
The issue is that the hotas is about 30mm too high to just set on a desk which you'd normally be fine typing or mousing at, so as others have said, you need to lower the desk, or otherwise find a way to lower the stick and throttle to at least where the top of the body of the stick/throttle is at desk height, if not, even a bit lower. Take a look at things which use joysticks (e.g cranes and diggers) and you'll notice that the sticks are generally a little above the knee.
I also toyed with positioning the stick and throttle at butt level either side of me, it was comfortable but impractical.
The other advice about exercise is probably useful too, unfortunately I'm allergic to that kind of thing. Its medical. Bones in my leg or something.
