That’s not a slow laptop. I’ve been daily driving worse for years.
To protect the data from random thief just browsing through the files I still use ecryptfs. It only encrypts the home directory, and the keys are derived from my accounts password, so no extra hassle.
The encryption is weak by the current standards, and wouldn’t stop a determined attacker, but it’s 100% better than nothing, and I’ve never noticed any performance problems.
One could argue the vests are like seat belts in a car. You don’t need them 99.9% of the time.