Waking up with back pain, trying to hold off on a new mattress until I move in about a month. Any (frugal) suggestions until then?

Hello Reddit! As the title says, we just bought our first house, and it’s a great time to take my current mattress and put it in a guest bedroom, and splurge a little more on my own (still frugal though, as a house is expensive!) I have been waking up stiff and sore, and I’ve tried foam toppers, new pillow, pillow between legs in various positions etc., so I am now convinced it’s our mattress. I didn’t have these issues before we moved across the country and left our old one behind. I don’t recall the exact brand of my current mattress, just that we got it from Walmart 3 years ago and that it had decent reviews. My husband has no issues sleeping and is of average height/weight. I’m small, and I do powerlifting, but I haven’t lifted heavy in weeks and I’m seeing no improvement.

Any suggestions on improving my sleep while I’m trying to wait for the better timing of a new mattress? Any mattress suggestions would be helpful too. I did some research already and was leaning toward a Zinus one. As you can see, I am trying to do this frugally, but I do understand that sleep is so important and not something to cheap out on.

Thanks in advance for listening!