You can use my extension yii2-widgets and refer the input group addons section which simplifies this for ActiveForm and ActiveField for all bootstrap form orientations (horizontal, vertical, or inline). If you are using the extension, its as simple as typing :[s]
Alternatively, if you do not want to use the extension, you can pass the template property to style as per your required input-group. You will need to then do this for every text input field where you need this.
[size="4"]NOTE: This extension has been upgraded and the new syntax for addons is mentioned here[/size]