gistfile1.php

function wcs_redirect_product_based ( $order_id ){
	$order = wc_get_order( $order_id );
 
	foreach( $order->get_items() as $item ) {
		$_product = wc_get_product( $item['product_id'] );
		// Add whatever product id you want here
		if ( $item['product_id'] == 70 ) {
			// change to the URL that you want to send your customer to  
                	wp_redirect('http://www.yoururl.com/your-thank-you-page');
		}
	}
}
add_action( 'woocommerce_thankyou', 'wcs_redirect_product_based' );