I use wood chips in all my pens and houses. It has several advantages - the aromatic wood and leaves from eucalypts and melaleucas etc tend to repel insect pests, and the big one is it is free - the local council has several
wood chip dumps around the shire where they leave all the mulch from their tree pruning operations.
I don't get mine free, but I have a truck load delivered for the gardens each year. For my boggy pen I put a bed of straw down then covered it with pine bark . Once every now and again I top it up. I'm still keen to try pine needles, they say it also has acts as a natural insecticide . How's the weather in your end of the woods Ash ?