Lower back exercises

I was wondering if anyone here has tips on how to strenghten lowe back muscles.

I have curved back and I decided it would not be a bad idea to do something about it. When I was a teenager, I had a scoliosis. I was going to a doctor to show me some exercises. I'm not sure if I still have scoliosis even now (although I may), my bigger problem (at least I think) is what I found is called saddleback or too pronounced lordosis. I've always had my buttocks too pronounced and I have a hard time getting my spine straight, be it while standing on lying on the floor. Recently my kobudo teacher keeps reminding me to not stick the butt out and to align the back so I don't have pains later. But it's easier said than done. I just can't. And when focusing on it, when tired and lifting something heavy, I tend to compensate the weight by curving the lower back even more. I don't have any pains, exept sometimes after a night's sleep on my matress that I'm going to change soon.
But I wonder: does anyone have tips on how to strenghten the lower back musles? Which is probably what should help... I googled a little, but I mostly found only stretches (some of which I do anyway) or stuff like squats, push-ups etc., which is something I do as well, though can do more. And I didn't see any difference in these few years. I know the obvious choice if I really want to do something about it would be to visit a specialist, but I'd rather (at least at first) tried some exercising at home. So I also don't mean deadlifting or working with big weights. Any thoughts would be most appreciated. :)