I had very little luck with the K pouch, I wish I had just gone straight to the permanent bag in hindsight. If you are truly ready to be done with pouchitis and all those complications, I would just embrace the ostomy. With regards to your initial question. I had very little pain in the butt / rectal area. it was just the usual pain with the incision. I was expecting it to hurt to sit, and all that, but I didn't have that problem at all.
Good luck!