Therefore we have to make a decision that seems best for them, even considering our cultural bias and imperfect view of their society. I can even say that we will make a decision for them, maybe just wrapping it into some feel-good distractions. When you decide not to interfere you're not really letting them evolve on their own, you're starting to avoid them. It's more subtle influence, but influence nonetheless.
I'm not really saying that change is inherently good, that's a view that can be easily disproved by samples from our own culture. I'm saying that change is an inseparable part of culture, and we shouldn't try too much to protect a culture from it (but we shouldn't actively try to destroy a culture without very good reasons -- like, I don't know, mass killings or something -- as well). Especially considering that (at least for me) people are more important than culture (while keeping in mind that culture is quite important for people).
As for preferences like those you've mentioned -- actually, here in Poland I know people from the whole spectrum on each of those issues, and soft mattresses are easily available. When you don't show a person a mattress you're not really letting the person choose to sleep on a bare floor, you're forcing the person to sleep on a bare floor.
Their very definition of comfort might be different from yours. Keep in mind that many people in more advanced countries prefer heat and humidity, sleeping on bare floors to soft mattresses, and many other things that many other people would consider odd.
Our culture is about change, many cultures are about tradition. Change is not inherently good.