I would recommend visiting a few different dojos teaching different martial arts, and watching a class (most will let you do that) to see if it looks like something you'd feel comfortable with.
If you're looking for something fairly gentle, you might want to check out Tai Chi (as someone else recommended) or Aikido. If you're looking for something a little more hard-edged, maybe Karate, Ju-Jitsu or Kung Fu (Wing Chun style is supposed to be particularly good for women).
Personally, I found I got more benefit from the hard styles than the soft ones (Ju-Jitsu is what I stuck with for the longest) - they required me to push myself more and ended up giving me a lot more strength and confidence. If you're trying to break out of your usual habits and expand your boundaries, sometimes something that pushes you further out of your comfort zone is best. But everyone is different, and checking out several different things is the best way to get a sense of what might work for you.
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If you're looking for something fairly gentle, you might want to check out Tai Chi (as someone else recommended) or Aikido. If you're looking for something a little more hard-edged, maybe Karate, Ju-Jitsu or Kung Fu (Wing Chun style is supposed to be particularly good for women).
Personally, I found I got more benefit from the hard styles than the soft ones (Ju-Jitsu is what I stuck with for the longest) - they required me to push myself more and ended up giving me a lot more strength and confidence. If you're trying to break out of your usual habits and expand your boundaries, sometimes something that pushes you further out of your comfort zone is best. But everyone is different, and checking out several different things is the best way to get a sense of what might work for you.