Gmail Button allows you to add a toolbar button to your Gmail inbox. You can use this in lieu of a sidebar bookmark or toolbar bookmark simply by dragging it to the Menu or Navibar.
P.S. If you open Gmail from a bookmark, you can go straight to New Mail by replacing the target to:
https://mail.google.com/mail/?zx=kksynt1xtviu&shva=1#search/is%3Aunread+in%3Ainbox