i once had a laptop with a mechanical slider that could cover the camera, that was ideal
my current one has a hard switch, that works too

honestly i don't bother with stickers anymore because i use my cameras too often, especially on my phone it's one of the main things i use my phone for at all 

 There are some phone cases with flip covers too.

Do you take selfies frequently? If not, then at least the front camera can be covered without too much friction.