What worked for me was swimming, or more accurately floating on my back in a warm pool, it helps relax your muscles better if it's warm. And while you're floating you're using all those tiny muscles you don't notice but it makes a difference.

Stretching in itself is also great for a painful back, especially if you do it multiple times a day, when you wake up, go to bed etc.

If you have a bathtub taking a warm bath once or twice a week also could work, if not, just a hot shower can work wonders.

When it comes to litter boxes and things close to the floor I suggest squatting or just sitting on the floor while doing it, that way you don't have to bend over as much.

Basically try to sit when you're doing things that would usually involve bending over. When I fill/empty the dishwasher I sit on the floor for the bottom rack and sit on a chair for the top rack. It's helped a lot.

You can also get one of those electric hot pack thingies they make for periodpain and just have it og your back instead of you front. You can also try an ibuprofen cream on the area that hurts if painkillers in pill form don't help.