Fitch is great for holding tunnels
It's recycled food grade paper and perfectly safe. I have read that layering hay and a couple of other substrates is supposed to help tunnels hold but sounds rather complicated and hamsters are quirky and messy sometimes!
I've been using fitch for years and get the 10kg bag - lasts for months. I would just try mixing two substrates - or try fitch on its own. Some people mix fitch and finacard.
Fitch First - Fitch Paper 10kg Single Bale Bedding For Smaller Critters - Pet Bedding in Bulk - Pet Store
FinaCARD Shredded Cardboard Animal Bedding : Finacard, Dust free animal bedding for rodents, cavies, equines and felines