Yes the small of the back is of extreme importance.
GoodMorning's have shown to be a prime movement for the development of the total chain of rear muscles, from the upper traps down to the calves and ankles. Another version is sitting on the edge of a bench (bolted to floor of course) and doing GM's that way. More of a direct focus on that lower hinge of the lower back and hip structure. Powerful abs can also be a great help with squatting, front or regular, they assist to stable that lower back. Weaker abs may also have a bearing on some lower back problems when squatting.
SLDL's are similar but not quite the same as GM's. Adding a shrug motion at the top position, each rep, is done by some men. With regards to the GM's and SLDL's, I would favor the Romanian DL over both...just my view and results I get. By all means, do what gives your individual best results.
Just to note: Seem many Olympic lifters (some in the lighter classes ((87kg down)) do reps/sets with squat cleans from 300 to 400 plus in regular workouts. Some going down to the lowest point possible. Much more when bar is taken off a rack. Front squats, excellent way to develop that teardrop affect on the legs.
Good Luck.