Should I get full memory foam or one with springs for children?

Hi Ken.

The mattress should be right for the user (your daughters) based on weight and usage, not particularly the bed.

I personally would opt for the spring and memory foam construction for teenagers, but either will be suitable. As long as the springs are pocket springs, if not then i would opt for just the solid memory foam mattresses.

Remember to make an effort to bridge the slats with MDF or hardboard.

Kind Regards Gary