Which mattress is best for someone waking up in the night from back pain?

Depends: Most mattresses that are firm and supportive usually work the best but sometimes it depends on where back pain is. Usually a firm mattress with memory foam layer on top is best.

What feels best: The best mattress is the one which makes you feel the best upon wakening. Thus it doesn't matter whether it's hard, soft, or somewhere in between. What matters is how the mattress makes you feel and function.

No best: Despite what the mattress companies would have you believe, there is no such thing as best. A couple of general points, find a mattress that is neither too soft or too firm. Change your mattress if possible every 10 years.

Mattress: A firm mattress that does not sag is always better. Position and size of the pillow is also very important. Pillow should support the neck as well as the head and not just the head. Your sleeping position is usually the main culprit. Poor sleep has several causes.