Traditional wisdom put forth from the 1940s through the 1990s said "The firmer the mattress, the better it is". This was widely repeated, and accepted, but was never actually accurate. Today, people are developing a better understanding of what the mattress choices are for them, personally.

That's really what it is all about. Mattresses are a personal taste. Comfort and quality combined with your budget, are the two most important factors when choosing your mattress. Is the mattress comfortable to you? If it is not, you won't sleep on it. Tossing and turning, because somebody else said you should sleep on a brick, is not a good solution.

One of the most important steps in buying a mattress is actually trying it out. Controlled tests have shown that, on average, within 5 minutes, a consumer can determine if a particular mattress is acceptable to them. New technology mattresses may take slightly longer for the customer to adapt to, or determine their personal issues with. Most good stores welcome their customers trying out the mattresses. Be wary of side of the road or mail order dealers where you cannot sample the merchandise!

For example, the latest high-tech (higher priced) blow up adjustable firmness beds may feel extremely comfortable to a couple when laid on individually. If, however, they do not lay on them as a couple, they may miss the fact that having two sides of a bed at different firmness levels leads to a "mountain/valley" problem. Some couples do not find this disturbing, many do. So the primary issue again comes down to what feels good to the people who are going to sleep on them.
This is why visco-elastic memory foam, gel infused, and individually pocketed coil beds have become so popular. The beds (if properly constructed) adapt themselves to the each sleeper. It is important that you find a store you feel comfortable working with and people who will be able to discuss the mattresses with you. Then try out various units until one suits your comfort level.

There is a very good blog review that can help you to pre-choose a mattress before you try them out, this is courtesy of "Jen Reviews",
How to Choose a Mattress, According to Science – 9 Factors to Consider