Thanks for your question Olga. The answer to this depends on a few things, starting with what kind of back pain you mean. For now, I will assume you mean lower back pain, which is typically caused by your spine not being held in a properly aligned position during the night. Having your spine properly aligned is a matter of finding a mattress that matches your body and sleep preferences. There are mattresses that are too soft to provide you with proper spinal alignment, but there are also mattresses that are too firm to do so, as you can see here. And likewise, the mattress that does the best job providing proper spinal alignment for you might not be the same one that does so for your friend.

Now, in terms of the right level of softness for you, the biggest factor is your predominant sleep position. Mattresses with more softness will conform more to your body and allow the heaviest part of your body (the hips) to sink furthest into the mattress. If you sleep predominantly on your stomach, this can be a big problem, because your back can over-arch, meaning you will almost surely wake up with lower back pain. Likewise, back sleepers will experience a bit of a "hammocking" effect on a mattress that is too soft, which means that the lumbar area of their spine (the curve at the base of the spine) is not properly supported -- this too can cause back pain. Side sleepers need the most softness because the sides of your body have the most curves, so in order for your spine to be properly aligned, your hips actually need to sink into the mattress a bit.

Other factors that affect this equation are your weight and body shape. A very lightweight person needs the most softness, because even a medium firm mattress won't sink in for them enough to feel soft. By contrast, a very heavy person can will sink right through a bunch of soft layers (called "bottoming out"), so they need the least softness. Likewise, people with more curves may need a bit more softness to accommodate and conform to these curves.

Lastly, it is worth adding that proper spinal alignment is not the only factor that goes into determining your ideal level of softness. Most notably, you will also want to consider pressure relief. Pressure relief is how a surface disperses your weight as broadly and evenly as possible over the surface of your body. Softness can help with pressure relief, and mattresses with inadequate pressure relief can cause you to feel "pressure points" in the parts of your body that are bearing the most weight on the mattress. If you've ever woken up during the night and noticed a sharp pain in your shoulder or hip when sleeping on your side, or noticed that your arm or leg has fallen asleep, this means that your mattress is not providing sufficient pressure relief. So, you want to find a mattress that provides a proper balance between spinal alignment and pressure relief.

Balancing all the competing factors when choosing a mattress can be a bit tricky, especially if you have a partner to consider as well. If you have not already done so, I would recommend taking our match quiz, which will weigh all the relevant factors to determine the optimal level of softness for you. It will also show you mattress types available in your area that are a good match for your needs and preferences.