Hello Dries
Interesting design you have come up with, gate wheels could do the job, I know. (have used them for a whole lot of apps) I think the flatpack kids furniture could work, just make sure to use good quality wood. Try approaching toy-zone or baby city first, they are not as sticky as the rest.
If you are based in the Pretoria area, you are more than welcome to attend a club meeting.
Cheers