need help with picking the perfect substrate!!!

so i own a beardie of course and all his life hes had 3-4 different substrates - plain old dirt, then a sand/powder mixture, then repti carpet (this was temporary!!) and now he has crushed walnut shell sand, which i heard can cause impaction, so im getting rid of it. as of now im trying to research the best substrate but im stuck between dirt or sand. can anyone advise the best brands to use? i was thinking Australian sand substrate, i want to make my baby as comfy and happy as possible