Hi,
you don't want to use AJAX, that is fine, but you don't want to use Javascript also ? I think you have go for javascript in order to show the notification alert message. but this message you can show from code behind also. check out below how:
ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "Notify", "alert('Data Inserted Successfully');", true);
you can change the message text however you need based on the conditions.
refer
ScriptManager.RegisterStartupScript Method (Page, Type, String, String, Boolean)[
^] for more.
hope it helps.