Buy $1,000 worth from Coinbase, assuming you have $1,000 to lose. Move it immediately to a paper wallet. Store the paper safely and forget about it for five years.
Paper should last longer in a firesafe than most digital devices and is quite a trustworthy device. Paper has an autoignition temperature of 450 degrees F, so a UL class 350 rated fire safe should keep your paper documents safe, but those temperatures might ruin digital storage devices.
I agree with everything you're saying except the paper wallet.
This insanity surrounding: "store your fortune on a piece of paper under you mattress/buried in your backyard/etc" has got to stop. Pay coinbase to do that for you.
But that is the essence of Bitcoin, and indeed of any encryption: ultimately you're responsible for keeping some sequence of bits secret from everyone else in the world. Encryption doesn't help with that ultimate problem, because the key to decrypt must be held in cleartext. If you keep the data online, you're simply moving the responsibility of protecting those bits to another set of bits (your passphrase/OTP for the online service). If you keep the data on a machine-readable medium such as a USB drive, you're trusting that the flash memory's floating-gate transistors will keep their state longer than you need. If the medium is a spinning drive of any kind, you're trusting that the moving parts will still work. If it's a less volatile medium like a CD-R, then you're trusting that you'll still have a device capable of reading the physical medium and the filesystem in the future.
Today, your fortune is either (1) bits you protect through physical custody (including your password manager's master passphrase that you have memorized (or "buried" in the mattress/back yard of your brain, if you will) -- and what are you going to do to pass that passphrase on to your successors when you die?) or else (2) trust in institutions such as your bank, your employer, your county recorder, and Coinbase that they'll honor your claim to the rights/property they manage for you. Bitcoin gives you the _option_ to eliminate (2) and rely only on (1). You're right that you don't need to eliminate (2) if doing so doesn't interest you. But even if you do choose to rely on (2), you still have no choice but to use (1) as well for at least _some_ of your secrets.
For whatever that set of secrets is for (1) -- especially when the question of inheritability is addressed -- ink written on paper is a very good solution.
Not controlling your private keys is inherently unsafe. I have several copies of my (encrypted) paper wallet that I distributed among friends and family.
