Usually changing the FOV helps people with motion sickness. You might want to increase it to something like 90, 100, or even 110 (if you're using a widescreen monitor). The screen size might be affecting you. Maybe playing it on a larger or smaller screen would help.
Sometimes removing headbob helps, but Mirror's Edge pretty much did that (although there is a slight head sway).
The developers actually tried to reduce motion sickness as much as possible. That's even why they added the dot in the center of the screen, which gives you something to focus on to help you avoid getting dizzy (a trick they learned by interviewing ballerinas).
There is a way to enable third person mode, which might help, but you can't look up/down and the animations are a little stiff.
Disabling motion blur may also help.
Here are some suggestions I found on online that don't involve modding the game:
-Turn on more lights.
-Sit farther away from the TV.
-Your body can get used to it after repeated sessions—a pattern of playing and getting sick, stopping, and then restarting later when you feel better. Do this until you stop getting sick entirely and your brain finally realizes that what you are seeing and doing isn’t actually harming you. That process of getting used to it can take a while and isn’t pleasant, however.
-Some medications can help (Dramamine, Bonine, Meclizine, and Benadryl), and while they can work, they might also make you drowsy, which isn't good for gamers and most people in general.
-Sit up straight / put a pillow under your lower back.
-open a window / door / turn on a fan to cool down
I do understand what you're going through though. I couldn't play Halo 2. The muzzle flashes were huge and too bright in that game. I couldn't play that game without getting headaches. Sadly, there's no way to train my body to get used to that.