The lap tray/keyboard/mousepad thing doesn't appeal to me at all. When using a computer from the armchair I have a cheap wireless Logitech K230 keyboard and basic wireless mouse. Mouse is on a small table next to the chair, keyboard on my knees.
The keyboard isn't going to compete with a mechanical, but it's very agreeable for HT and we browsing, replying to discussions etc. I won't be too upset if it gets dropped or is on the wrong end of a spillage. For lengthy typing I'd want to be at the desk anyway.
For a some gaming I like the idea of the split keyboard, it doesn't have to be an Ergodox but I can imagine having a similar table each side of the chair similar to how I use the mouse now.
If none of this appeals and you still want similar product to the Roccat but for adults, then try searching your preferred stores for "lapdesk" and "lap tray keyboard." Otherwise you might try investigating the likes of Ergotron or Humanscale for a suitable arm with keyboard tray attachment.