For climbing, have you tried Popsicle/lolli stick or poplar dowel platforms? I've seen some really nice ones and they can be fairly sturdy if you design them right
My friend has a Syrian who loves to climb and she built several platforms out of them and her ham absolutely loved it! Here's an example (I think someone posted this on HC a while back, but I couldn't find the original post so here's the Pinterest one)
https://s-media-cache-ak0.pinimg.com...5f7713276f.jpg
If you're DIY savvy, you may be able to make something like this