I’m not a parent, but going by pop culture, it seems like literally every child has the same fears.
In pre-modern times, I imagine that they’d be sleeping in the same room as the parents, but if modern notions of privacy don’t permit that, seems we could at least design an enclosed capsule or something.
It is an opportunity to bind with your child. Make them face their fears playfully. Probably will strenghten its braverity.
Also, any matress needs air circulation beneath below it. Otherwise it will get warm, stinky and very dirty.
There are a lot of bed frames that are solid, though, including the one I use at home. If it causes any ill effects on the mattress I haven’t observed it personally.
Nonnative tounge - I meant below grabsthetoolbox