If you want to change to a double, you'd have to replace the front derailleur, the left-side brifter, and the crankset obviously. If you're just going to 9 speeds again, I would encourage you to think it over a little more - the performance gain you would be able to get from a properly adjusted 105 setup to Ultegra is minimal. And you'd have to spend a lot of money on the whole conversion; the new STI lever will cost you around $100 and the crankset around $150, not to mention a new FD for $30-40 or so. I'm not too sure what you were asking in your first question though, so I could be missing something.