Hi!
A couple of good options for a freestyle/playboat would be one os these;
1. Pyrahna JED-i in Small or Molon in Small
2. Jackson Star w/ possible some mods to accommodate height.
At 45 kg. Jack should be able to fit into a lot of smaller playboats. He's (like me) is at that weird stage
when he is probably in between the true kid's boats and smaller adult-sized boats. The best thing is to
go with the boat that is slightly large, rather than the smaller. You can always grow into a boat.
I would demo some boats before buying one. If you can demo one or two or three for a weekend and
spend some quality time in the boats, you can figure out which one will work best. The nice thing about playboating
is that it teaches you to think 3-dimensionally and to become comfortable at any angle, upside down or right-side up
or sideways. When you play in the hole, you lose the fear of the hole.
I tried out the Pyrahna JED this summer and was able to cartwheel it, even a couple of airwheels.
Hope this helps!
H-Bomb