If you side sleep, I don't think you'll run into too much trouble. To be sure, lay on your side and ask someone to check your spine is straight. Your hips should sink in a bit, but not too much.
Else, if you are a back or tummy sleeper and it's squishy, you should try to switch to something more firm.
If what I suggested is too radical, try natural latex, which is quite firm.
A good entry point to the (pretty lacking) sleep ergonomics literature is:
I actually sleep on my back. Not that I don't believe you, but why should I try something firmer when I find this mattress to be very comfortable and never feel back pain? I assume that this causes a risk of future back pain - would you have any information about that specifically?
Else, if you are a back or tummy sleeper and it's squishy, you should try to switch to something more firm.
If what I suggested is too radical, try natural latex, which is quite firm.
A good entry point to the (pretty lacking) sleep ergonomics literature is:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1119282/