If you're going to use bitcoin core as your main wallet then keep your computer from malicious files by installing strong and premium anti-virus (windows and mac).

And if possible follow the first reply for keeping your private keys offline while the watch-only address online but of course it require another computer.

But if you have a spare to buy hardware wallet, then I suggest buying it such as ledger nano s and trezor. And keep your bitcoin core sync as your contribution and support to the network.