... that a bitcoin capital will be fully kept in shape after 5 years:
you can either go with paper wallet or hardware wallet, web/online wallet and exchange wallet is definitely out of the question
Brain wallet would be the superior option because no one could ever find any physical copy of your key, this is assuming you have a functioning brain that won't forget what the words are in the future. Your brain can't be hacked or stolen.
that is actually the worst wallet to consider, brain wallets are not as secure as you thought yes your brain can't be hacked but a $5 wrench attack can make you spill out the words
and even if you didn't give it out, a hit on your head by that wrench can damage your brain
