I'm going to throw this out in the For-What-It's-Worth category re your sciatic nerve/lower back pain struggle...
It almost ruined a couple of York trips for me not long ago. At its worst I nearly cried just sitting in the driver's seat of the RV for the 10-hour run to-and-from York...but I was determined to make the trip.
I had/have (haven't been to him for more than a year now!) an excellent chiropractor who helped me through the ordeal as best he could. One day we talked about mattresses...what we're sleeping on. Turns out, he's a HUGE advocate of the Memory Foam genre, Tempurpedic in particular. About two years ago we upgraded our RV (our rolling York home!) and the new one had a memory foam mattress on the bed. HOLY MOLY! What a change in that first night's sleep!!!
Fast forward to the next few months....ditched our home mattress for a new I-Comfort (Serta) memory foam mattress... Now, almost a year later....I've pretty much forgotten I ever had the lower back pain....IT'S ESSENTIALLY GONE!!!
OK, what does this have to do with trains??? DUH!! EVERYTHING!!!! I never realized how much the ol' back is a part of this hobby...from crawling under the benchwork to do wiring, to walking a few miles through the aisles of York.
Even better....the wife is raving about her own sleep quality in the new mattress!
I know that this is not the answer for everyone, but your concern struck a nerve (pun intended!!!) Meanwhile, as others have said, you are among many empathetic friends at the York meet. Most vendors would gladly loan you a chair if you needed one in a pinch (...whoops, another pun!), but there are LOTS of places to rest anyway.
Don't let this keep you from York...especially for that first time!! You have a lot of us that have experienced what your suffering...and the 'York experience' will greatly reward you for the effort as we can testify!!
And may God bless you with healing...SOON!
KD