All of the above and stop every hour max to get off and take a stretch and walk.
A fitted seat from Mean City is a must for bad backs.

 

I've had 7 back related surgeries, the last being a 6 level 360 fusion
with 2 titanium rods, 13 pedicle screws, 2 plates, etc.
Took me a few years to get back to riding, but I was determined.
I can't ride much more than 50 miles without being in way too much pain,
but at lest I'm having fun when I can do it.
My Mustang backrest has been the best thing I have bought for the back! 10" mini apes, helped some too.
The contant pain has ruined my life, but at least I can still have some fun
when on my bike...
Oh, and if anyone is considering have back surgery simply to relieve pain,
DO NOT DO IT!! If they say they can cure your pain, THEY ARE LYING!!
I learned this the hard way, and now am stuck with enough steel in me to start my own junkyard...And after all that, the pain is worse now!!
I admit, some surgeries may help with sciatica, if you have a totally blown disk or something, but general back pain is NOT cured with surgery!

ok, i'm done...
Peace!