Maybe look on amazon for sheets of balsa, or similar?
I've also seen sheets of craft wood at dollar stores, and as long as the hamster doesn't chew it, it'd probably be okay.
Sorry if this isn't much help haha.
Thanks for the suggestions! I’ve had a look at balsa sheets on Amazon and HobbyCraft, however the main problem is that because they are designed for small craft projects, I can’t find any the right size. The largest platform needs to be around 50cm long and at the widest point around 25cm (I think) for the dig box. And most either come in tiny sheets or long strips. Do you know of anywhere that sells larger ones?
What is confusing me, is the platforms I’ve seen people build in the UK, are all made of plywood. Which normally is unsafe from my understanding, so I’m not sure where they have sourced safe types from. By all means I’d love to support these people by buying the ones they’ve made, but unfortunately I’d rather not spend £50+ on all the different platforms, most of which wouldn’t fit the specifications of size and bedding depth I need.