This is how i keep my private keys safe since i can't afford to buy a hardware wallet.
1. A complete new harddisk
I bought a new harddisk and install window 7 on it and copy all my private keys in there, i don't bother to leave this harddisk in the pc, after the copy is completed i remove the harddisk and keep it.
2.My Recording book
I have a long hard shelled book that i use for keeping records of all the airdrops and bounties i promoted because sometimes i used to forget easily so i write down my recovery seeds in this book as well
3. Flash Drive
I have a good 8gig flash drive as well that i use to copy software and files from one pc to another so i format this flash drive and copy my private keys and recovery seeds in it.
At first no one knew i am into crypto stuffs and secondly i don't share my room with anyone cos i am living alone, those who have people around them with face problems like friends going behind your back checking through your stuffs or even stealing your things, hardware wallet is still the best though.
Good to see that this works for you. However, of might not work for everyone. It is also good you admitted that hardware wallet is the best.
Also, if you can afford to buy another hard disk coupled with a good flash drive, you should be able to purchase a Trezor wallet, because it is not so expensive.
It is much safer to use a hardware wallet, because your external hard disk and flash drive can be corrupted with malware, which might lead to loss of information.