A mattress should be hard enough to support you, and shft enough to take your shape so you have al over support.
My joints are quite bad, 15 years of ballet.
I need quite a firm bed, because i need the support.
But i'm only 5' tall, just, and weight 8st.
I don't have the weight on me to press into these firm matresses.
I have a foam one now, it works wonderfully.
I used to have an individually pocket sprung matress. That worked great for about 8 years.
You spend so much time in your bed, ahem, at least 1/3rd of your life.
It has to be confortable, and supportive.
I'm no doctor, so i can't say if it is or isn't. But it can't be helping.
Buy the best, and most comfortable one you can afford. They do last, and they are a good investment.