Since you saddle is not either fullly forward or rearward, you have some leeway. Your's looks like a normal or 25 mm offset saddle. Those are easy to come by, but 15 mm and 30+ mm posts will also likely work. I would just avoid any zero setback posts. And measure the current distance from the mose of your saddle to the handlebars before dismantling. Also the saddle height drom the BB.