prioritising excercises

Like most people i try to put the hardest/ heaviest excercises first but ive started doing my bar bell rows the same day as my stiff leg deadlifts, i figured doing the SL's first is best as their heavier but when it comes to doing my rows my lower backs not man enough to suport the load, so should i change the barbell for a dumbell so i can lean on a bench and giv my lower back some suport or should i do the barbell rows first, or just do them on seperate days (that would mess the push/pull/legs thing im trying though)

you could do them chest supported i suppose

what i would do is lie on an incline bench and use a DB in each hand