AFAIK, there isn't much difference between the safety level of:
- a paper wallet
- a cold (offline) wallet
- a hardware wallet
the difference is in the price and usability.
- a paper wallet is allmost free (the cost of a piece of paper), but can only be used to collect unspent outputs. When you need the funds, you have to sweep the paper wallet and throw it away. It's also a bit tricky to make a paper wallet in the correct way
- a cold (offline) wallet costs a lot more, since you need an old PC that can never be connected to the internet as soon as you start using it to store your funds. However, if you set it up correctly, it's not that hard to use, and you can send and receive as much as you want, but you can also access the full feature set (like signing messages, creating raw transactions, broadcasting,...)
- a hardware wallet (trezor, ledger nano S,...) is actually pretty cheap, can be used to send and receive, can usually be used in different places,... It is my personal favorite. you are bound by some restrictions tough (for example, if you use the official ledger chrome plugin, it can not be used to sign messages)
thank you, now I know how to store my bitcoin safely, I just lost 0.5btc yesterday.