I'm thinking of buying myself a separate head for my wife's expensive electric toothbrush
Will your wife find out if you buy her a separate toothbrush head?
I hope not. It'll make my life so much easier.
It's okay if you don't want to share tooth brush heads with your wife. It's better for hygiene ways. Just be sure you explain to her why because if she finds out you went behind her back, she might be annoyed for a bit.
How should I put it? Maybe I should just say I didn't like her dirty toothbrush.
It is normal to not share toothbrushes. Maybe you can buy your own toothbrush and use that.