If you're not storing all to many documents I would recommend getting a fireproof bag, its cheaper and u can get one that is waterproof as well. I got this one since it has the highest heat protection on amazon but yeah a bag obviously wont do the job if you have tons of files to store :/
If I were u id buy a fireproof bag, they do the job if u get the right one. This was the most fire resistant i could find on amazon. But I mean if you have loooads of stuff to store then get a safe but if its only for documents then get a bag.