the safest wallet is the offline wallet but there is still a risk that if the pc where you keep the offline wallet is destroyed then you can not do anything
Yeah that's why hardware wallet is the safest yet more secured from anything else. Try ledger nano or trezor, it's quite pricey but at least you're coins are all safe especially when you really have a lot. While using flash drive is also safe but there's a chance that it'll get corrupted.