You can install the add-on Products.ContentWellPortlets and replace the top-viewlets with portlets, by adding a portlets.xml in one of your add-on's profiles.
This example adds a logo and an image next to it:
<?xml version ="1.0"?>
<portlets>
 <!-- Assign Logo-portlet to site-root (key='/'): -->
 <assignment name="top" category="context" key="/"
    manager="ContentWellPortlets.InHeaderPortletManager1"
    type="plone.portlet.static.Static" visible="True">
  <!--
   Give this portlet a name, so we can recognize it easily in the
   portlet-management-UI via `[PLONESITE_URL]/manage-portletsinheader`:
   -->
  <property name="header">Logo</property>
  <!-- But don't show its header and footer when viewing the portlet: -->
  <property name="omit_border">True</property>
  <!-- Replace 'Plone' with your site-id here, in case it differs: -->
  <property name="text">
     <a href="/Plone">
       <img src="logo.png" />
     </a>
   </property>
 </assignment>
 <!-- Assign another portlet in next column (InHeaderPortletManager2): -->
 <assignment name="top" category="context" key="/"
    manager="ContentWellPortlets.InHeaderPortletManager2"
    type="plone.portlet.static.Static" visible="True">
  <property name="header">Some image next to Logo</property>
  <property name="omit_border">True</property>
  <property name="text">
    <img src="defaultUser.png"
        title="Dummy-user-avatar" />
   </property>
 </assignment>
</portlets>
And polish it with some styling.
For the search-box I'd may assign a search-portlet above the content (using ContentWellPortlets), give it a minus-margin-top and for the globnav a margin-right, but as there's many ways to Rome, I'd might replace the globnav with a navigation-portlet, too.
Here's an add-on for illustration-purposes (see its viewlets.xml on how to hide the top-viewlets):https://github.com/ida/adi/tree/master/adi.samplestructure