I'd recommend trying out DeleD (http://www.delgine.com/). It's not the greatest program by any means, but if all you want to do is convert an .obj to a .mesh, it works just fine! It's fairly simplistic and easy to navigate. Just make sure that you download the Ogre Exporter extension along with it (I think it might come with the Ogre exporter by default, but I'm not 100% sure. If not, the download for that is HERE (http://www.delgine.com/plugins/viewPlugin.php?catid=40&catdesc=Exporters&contentid=4)).
You should be able to import it under the Plugins tab at the top, labelled as "Wavefront Obj Importer".
(https://orig00.deviantart.net/00af/f/2018/162/5/e/deled1_by_torskite-dce5s1s.png)
If it's not there, you might have to install the plugin off the website, though I'm pretty sure its included with the program.