I have a couple of Putting aids that I like.
The Eye Line Putting Alignment mirror does a great job of helping shoulder alignment and eye position at address. It can also make you aware of excessive head movement during your stroke.
The Navigator by Dirty Larry Golf. This is great because it really helps with direction and also if your clubface is square at address and at impact.
If you’re not looking to spend much money, Alignment rods are still a great option. They are great for helping with direction and also gives you a reference point of how your stroke is moving back and through.