I had the same issue, But i just shaved the little lugs that connect the button to the switch with a scalpel and used the original plastic black cover. Works a treat and i’ve no fear the button will fall out.. :)
The top cover can be a little stubborn. There are locating clips on the edge opposite the screws that like to hang on. Use the force..
1mm should do fine. Guess metal over plastic, although the composites don’t deform under heat as you’d think they would…