After years of back problems and 2 surgeries including a fusion, the best thing I have found for backaches is moist heat, if your doc allows it. I take a bath towel, wet it down and wring it out as much as possible. Fold it to fit, then put it in the microwave for 1-2 minutes.
It will be *hot*. As soon as you can tolerate it, lay face down (if you can) with the towel on your back and cover it with a large garbage bag. The bag will retain the heat and moisture for 15-20 minutes.
I’ve done this for 15 years with great relief every time!