I like to put my seed phrase on a paper, if you want it safer, you can use a steel backup for it, there are steels that you can buy to backup your seed phrase and it is not a waste of money.
Instead of storing your keys on a piece of paper, how about you store them on a memory stick that can only be accessed via a password? I don't worry about a fire breaking out in my house because I always check the stove/oven every time I leave the house to make sure it's turned off and even check it during the day when no one else is around.
be careful that your method of storing your keys, is not so complicated that it will protect yourself in the end...