Eating a little from those toilet (clean of course) paper tubes is fine, and won't hurt him...eating a lot of cardboard is certainly not good though. Half the time they "chew" it up but don't actually swallow it. How much does he seem to be eating ?
Here are some safe toy options from our home page, for you to click out.
Guinea Pig Toys and Play
Tunnels are a really big hit with most piggies, and I have made some home made cardboard ones too. Another favourite is Fleece Forests. They love big piles of soft grass hay to run through. Paper bags. Shredded plain paper.
Providing enough space in their cage for running laps, optimizing what you do have by making sure to put their pigloos, wooden hidey's or cozies ect
towards the middle of their home so they have room to "run around" all the objects in their home for fun and great exercise.