If you want to invest in bitcoin, much like other investments, you need a long-term approach.
Swings will be heavy, but remember you are in for the long-term.
Now, provided your payment method is SEPA transfer, I advise to use an exchange like Kraken or Uphold. They have very low fees, i believe Kraken lowest, not that it matters a lot with the crazy volatility.
Send the euros, buy the bitcoins and then withdraw to your own wallets.
Bitcoin transactions are irreversible.
If you are not sure your computer is clean, well, clean it. Phones are more secure. Trezor is my wallet of choice.
If holding BTC is not enough risk for you, there are services that will offer interest for holding your bitcoin. P2P lending, margin-lending etc.
Needless to say, the risk great using those and the web is full of scams.