Best type of bed matress for child's back?

[samy23]

I need to get my 7yr old a new mattress for her bed, but want it to be a good one....however im not sure what to look for. Should it be soft or firm? or inbetween or what would you recommend?

[milkmamamerina]

My dad is a chiropractor. Firm is best, but it should be comfortable to your daughter as well, so if she can come along and try them (if that's at all practical) that would be good too.