Whatever you do Brock, eliminate movements that utilize bending at the waist...that includes sit ups...and that's why I like that incline bench/ball throw exercise for working my stomach core muscles...it works much more than just your abs and it forces work on your muscles fully extended which forces fuller development WITH ZERO BENDING
I have a bad back too Brock, not as bad as you tho, bro...
Pull ups work the back, underhand pullups will work back and Bi's off bodyweight and therefore eliminate injury/irritation by not picking up weight and also not bending to complete the exercise..Gyms have machines that take your weight too.
The Roman bench, the one where you under lock your heels and support your weight with your thighs leaning over the bench...bending over using that and then raising yourself to fully extension and holding the top position on each rep... that's an excellent back ecercise
And planks, forward facing the ground wrist below elbows weight on forearms and reverse planks, facing the ceiling, fingers forward palms down
Those exercises will strengthen your back with minimal impact