Ottoman bed - divan or sprung base?

I'm looking at replacing both bed and mattress. Definitely keen on getting an Ottoman for storage reasons, but one thing I can't find much on is whether a divan base is better than a sprung/slat base, and whether or not this depends on the mattress. Even if one isn't necessarily better, I would like to understand reasons for choosing one over the other. I'm leaning towards a pocket sprung mattress, though my wife suffers from sciatica, so if any mattress types are particularly good for this, I'd consider changing my mind.