Having a very bad back, the right mattress is essential. The only way to decide is to lie on it for a while.
I used the Choice survey and looked (from memory) for the mattresses with the highest satisfaction and lowest/lower number of problems.
Then go to the retailer (Ikea) and lie on different mattresses for a while with the spouse to work out the best one, and make sure it is OK for both of us. Wife woman likes softer mattress but will put up with hard 'slab of concrete' to support my back.
Spent over an hour lying on the final choice mattress before deciding to buy it. Came with a return guarantee if it didn't suit. (Didn't have to return it!)