Really? It doesn't sound that complex, unless I'm missing something here :-)
Your site still looks great and wow, super fast!
I would suggest using a theme like Responsive.
It doesn't look much aesthetically, but it's a great starter for a responsive site.
That theme could quickly be made to look like your site and has built in most of the 'responsiveness' you'd need to get started.
But it would require you to get dirty with the code. Depends on your skill level I guess. :-)
Good luck with the update!
Luke the Daft Duke
