Wait, now that I’m thinking about this (should have done this earliers, but is just popped up :-)) I can use a WP function to return the post id by using the slug!
function get_ID_by_slug($page_slug) {
$page = get_page_by_path($page_slug);
if ($page) {
return $page->ID;
}
else {
return null;
}
}