If you have the spare bales, this will work but they become quite rotten within a year and slump to less than half the original height, so new ones are needed on a regular basis, with the old ones added to the heap, but tending to bring quite a few dock and grass seeds I find.
Cardboard will help but it can go soggy; I break it into smaller pieces and use mostly brown, as shiny board rots poorly. Something more fibrous like old straw is better at holding some air in a heap. If you do end up with sogginess, turning the whole heap to admit air is a remedy, and covering with polythene to keep rain out, after a heap is finished.
Fleeces rot very slowly as the wool’s lanolin repels water and they definitely need tearing or cutting up, maybe with a rotary lawnmower? Good luck!