Hi tarnator,
The needs of children are quite different from the needs of adults and they will generally do better on a firmer mattress than an adult may be comfortable with. Post #2 here includes several links with more information about mattresses for children and some links to good sources .
The Ultimate Dreams could be a good choice but I would choose a firmer comfort layer than I would for an adult. This doesn’t mean that it should be so firm that it is intolerable for you … but it should probably be firmer than you would normally be comfortable with.
Phoenix