I'm long way down the road from my back surgery but I still try to baby it. Take it easy and slow. Do NOT ride anything you think might hurt your back, so not worth it. My SO is always making fun of me because for some reason riding the winnie pooh ride hurt my back. Yeah, I know lame. But it was something about the narrow seat and the bouncing or something. Better to be safe than sorry. Disney will be there in the long run, make sure your back can come back and visit!
Splash mountain was no problem for me, it's smooth, space mountain hurt and I won't ride it again. Neither will I ride big thunder mountain.