Books and backstores can be good resources. A rolled towel behind your lower back can be helpful. Static sitting is one of the worst things that you can do. It can be worse than even some of the most taxing sporting activities. Look for backstores in your community.
Most people think that when they get a back strain or sprain it is due to a muscle going bad.
The muscles then go into spasm for protection, so relaxing the muscles makes you feel good, but it takes away the element of protection, so you have to pay close attention not to accelerate the problem by using massage. Shiatsu would not be appropriate if the muscles are protecting a broken bone. Therapists and massage people do use elbows and use tremendous force which feels very good and can give you extended relief. Some techniques are much lighter. You must assign the massage to your condition.