Can't do Deads as I've got a fractured pelvis so can't load it up. Been doing some hyperextentions though, just wanted a bit more variety as they're getting boring lol. Most of the exercises I've been given seem to be yoga and I'm not sure how much strength they will bring?
Lots of core work will hit the lower back. Will give you loads of strength but little size. Look up hip thrusts for example. Can do it weighted or not. Off a bench or off a gym ball for extra core involvement.