@StrawCake- What I love about trundle beds for kids is that you can use the bottom portion for storage when you don’t need the mattress. My daughter has a twin trundle bed but instead of keeping a mattress in it, I just keep her toys in it and it keeps her room so organized.
She says that her dolls are going to sleep when she puts them back in the trundle. The only downside is that trundle beds for kids tend to be on the heavy side and little pricier than a traditional twin bed. I think that the extra cost is worth it because the peace of mind that you will have from an organized room is priceless.