one way of doing this is- first getting last date of current month and then adding 1 day to it, to get next month's first date. This will prevent us from unintentional skipping of months which occurs while using '+1 month'.
$today_date = date("Y-m-d");
$last_date_of_month=date('Y-m-t',strtotime($today_date);//get last date of current month
$last_day_of_month_proper =strtotime($last_day_of_month);
$new_date=date('Y-m-d', strtotime('+1 day',$last_day_of_month_proper));
echo $new_date;