Probably cold wallets. It now depends on your preferences which one exactly. But I think if you are holding quite a handful of bitcoins already you should consider using cold wallets. Less chances of being breached through internet scams. You just have to make it sure it is safe physically. Store it somewhere where it will not be easily stolen or forgotten by you. But even if someone had it, they would not be able to just open it easily. So it is still safe.