Broke a zipper on my Futon Mattress, what is the simplest cheapest solution to get it fixed?

it is worn out n old probably no more than 4", but my dog sleeps on it now and it is perfect bed for him to sleep like a Dog KIng

any cheap easy zips to zipper it up?
Update: no half a.ssed useless answers

how can I zip it up and shut so the fluff doesn't come out?
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