Back pain relief

I’m almost 15 weeks and my back pain has been horrible. I only have back pain after sleeping, so I’m guessing I need to change my mattress (it’s pretty soft/memory foam). I had read that the further along you get/more weight that starts to gain in your mid section that you should try a firmer mattress. But before I go out and get a new mattress (because they aren’t cheap!) I’m wondering anyone that had soft mattresses did anything for back pain relief that didn’t resort to buying a new mattress?? So far my pregnancy pillow doesn’t help, and every position I sleep in ends up in back pain. Any help would be appreciated!!