FOX - Currency Switcher Professional for WooCommerce

You should insert there not big drop-down. You can create currency drop-down in Smart Designer and set there smaller size elements (fonts, heights). Then install plugin ‘Shortcode in Menus‘ and place there SD shortcode:

Result will looks as shown on the next image:

To get more attractive variant use ‘scale‘ option!

• create new shortcode in Smart Designer
• set ‘scale‘ option there, for example 0.5
• open file functions.php of your current WordPress theme and place there next code:

  add_shortcode('woocs_menu_sw', function($args) {
      ob_start();
      ?>
      <div style="
           position: relative;
           top: 34px;
           margin-right: calc(500px * -0.5);
           "><?php echo do_shortcode('[woocs sd=9]') ?></div>
      <?php
      return ob_get_clean();
  });
  

• place shortcode [woocs_menu_sw] into main menu how described on the beginning of this article
• margin-right: 500px is width of the drop-down set in Smart Designer, 0.5 is ‘scale‘ option what set there
• top: play with this value, but approximately for scale 0.5 it is 34px

Result:

See demo site menu (width is 340px, scale 0.5). As you can see result using scale option is more accurate.