https://qiita.com/takaday/items/b992c7d8cd69343b6626
こちらの方法がとても良いです。
bootstrap/app.php
switch ($_SERVER['SERVER_NAME'] ?? 'localhost') {
case 'development.co.jp':
$app->loadEnvironmentFrom('.env.dev');
break;
case 'staging.co.jp':
$app->loadEnvironmentFrom('.env.stg');
break;
case 'production.co.jp':
$app->loadEnvironmentFrom('.env.prod');
break;
}