you can actually write or rather draw the QR code too. QR codes are just a big square that have small dots filled or empty to create the "picture". and for a private key with 32 bytes it won't be that big. you could also play around with the encoding (eg. use base43 or use all uppercase in bases like base16 that let it) and reduce the size even further.

in any case if the plan is to write down the key it is best to use an HD wallet and write down the mnemonic since they are words and easier to write down by hand compared to writing a key base58 characters.