Increasing security for your Bitcoin holdings is always easiest through using Paper Wallets. You do not need any expensive devices such as Trezor storage or any similarly fancy stuff. As long as you do it right, a Paper Wallet is the way to go.
You want to create paper wallets using an offline printer though. Ideal are dumb printers -- i e "old ones" that do not have wireless capabilities or similar securiy holes built in. Also make sure you disconnect your computer-to-internet connection while creating the private keys.
For additional Crypto coin security, you may also want to observe the following:
*never leave any Crypto amounts in an exchange, unless needed for trades (centralized point of attack/failure/general vulnerability!): you might want to remove your funds overnight and as soon as not held for orders
*move all portions of your Crypto coin savings to Cold Storage (meaning into an offline location, e g your paper wallet) and only keep smaller amounts needed for spending in a Desktop wallet, online wallets, or -- again -- those less-secure exchange portfolios etc.
That way, you are not only "your own bank" but (at least!!) as safe as one as well.
true, the good old paper wallet is the safest way -- upvoted!
Equally good seems an off-line SPC like RaspberryPi Model B (ideally without the added wireless functionality of the later models!) and/or secure backup of private keys onto durable MDisc storage.