Is there such a thing as a truly comfortable futon that won't give you back problems?

My personal experience with futons has not been good. They have thin mattresses on hard wooden slats. What’s to love? Consider another type of bed or a couch/bed.

Nope try getting a regular bed

If you put the futon mattress on the floor, the way they were intended to be, it will be comfortable. Sleeping on a frame with slats will not be.

You need to get a Futon that is a Mattress, not a pillow.

They won’t role or fold like a traditional Futon. But they can be might comfortable.
They will fold enough to be put on a couch frame.
I have one in my guest room. I have had no complaints. Have slept on it my self.

But, they are not cheep. You will be looking at $250 – $450.

A futon is a compromise. It’s not a comfortable couch, and its not a comfortable bed, but it functions in both ways adequately. I slept and sat on two different futons for a good 2 years on a regular basis and neither was entirely comfortable in either function.