Paper feed bags are good if you don't want cardboard. Ask anyone who buys feed in bags for chickens or goats, they probably have a bunch. No corrugations for the slugs to set up housekeeping in.
I do cardboard, I get huge boxes from the furniture store trash, be sure to clean up well after yourself (and them!) and no one will complain. It always looks better when I leave than when I got there. Weighting it down is required, it blows away fast as soon as it dries out. When I have cardboard down and no mulch on it yet, I drop T posts or bricks on it.
Fun story: I had a cop stop one day, he said "This is not a police question, just for my own curiosity. I see you get the cardboard out of the dumpsters, I see you strip off the tape and stuff, then you put it on the ground, WHY?! What are you doing?" I got to teach him about sheet mulching! That was in the desert, where the ground reflects a lot of heat, I had him walk where I had mulched, he said "It's 10 degrees cooler here!" Yup. That it is.