We are in the process of moving LO to a new bed-- he's been in a toddler bed since last year but we decided to change to a twin when he moves to his new room in a few weeks as we will need the crib mattress again

We will be giving up our guest room when Baby #2 arrives shortly and want to put LO on a trundle bed so we have the option of some additional sleeping space if we need it for visitors. Some of the beds we've looked at allow for two inner spring mattresses (the kind of trundle bed where the sleeping surfaces are on two separate levels) and some only accommodate foam/latex mattresses, stacked on top of each other.

I remember researching foam/latex mattresses in the past and had some hesitation about how good these are for growing children. If you had to choose, what kind of mattress would you choose for LO, for a potential long-term bed?