For iron I recommend strip mining at y level 16 meaning go to y 16 on bedrock click display cords on java press f3 and then just go straight that is iron

For diamonds same thing but -56 for the y level

For netherite you want to get some beds go to y 16 mine 6 blocks forward Place a bed Place a block behind the bed in-between you and the bed like deep slate so it is tough then right click on the bed