Sure, the paper wallet is the safest option, but how? For example, suppose I wanted to save a considerable amount of money in bitcoins (in my case I will take the example of R $ 100), so I have to let it all just in this paper wallet?
Paper wallets are a great form of storing BTC. The main security risk here is when you are creating them. If you are creating them on your daily used computer, it have a high chance of getting hacked as malwares can get your private key when you print it. Many people say linux is a better choice however, I think even windows would work fine if it is a not pirated. Do wipe your computer first before creating.
Trezor/raspberry pi is definitely safer than paper wallets as you can create a transaction offline from the raspberry pi and broadcast it from another computer without much hassle. Trezor isn't much of a worry since it doesn't have any widespread virus yet.