S.M.
I have only heard of coil mattresses. I do know that you can can different levels of firmness. This is important to consider id you plan to have more than one child. Matresses need to stay firm enough to last for a second baby (due to SIDS risk). I think part of the issue is how they are covered or what the outside material is since some people don't reuse mattresses due to worrying about how they trap bacteria, dust, etc. Most of the cheaper mattresses aren''t "rated" for reuse with a second child. We have a matress shich is firm on one chide for a toddler and extra firm on the other side for an infant and rated for reuse. We got it at Buy Buy Baby.
Anyway, if you are going to spend a little more, then look at whether you will be able to save the mattress and reuse it.