W.D.
If I had it to do over again, I would have bought my kids Sleep Number beds from the get go. They last for decades (my parents have had theirs for at least 20 years and we've had ours for at least 10 years). It might be more expensive at the outset, but it will likely be the only bed you need to buy them until they are adults.
The biggest advantage is that you can change them from soft to firm at the punch of a button. This is a huge plus because if, at some point, they decide they want a softer or firmer bed, you can change it at their whim without having to buy a new mattress.
.