My fitness level and flexibility are fairly poor and I would like to find a martial art that is complementary with yoga to help improve my overall physical wellbeing. Are there specific martial arts that would help me achieve this goal without aggravating sciatica?
The question asks which martial arts would improve sciatica.
First off, this sounds like a question for a physical therapist, not a collection of martial artists. Go to your doctor first. And you can easily google for exercises that improve sciatica as well as exercises that make it worse. Read up on what the medical community is saying first.
The main take-away from what I've seen out there is to simply exercise more to improve sciatica. That means pretty much any exercise and any martial art could help, with some precautions.
Martial arts that give you the biggest bang for the buck for sciatica might be those that exercise a full range of motion, especially those which flex the glutes and hamstring. And more importantly, they should not be high impact and should not result in loading the lower back.
A more gentle and relaxed martial art might be a good choice, one which still emphasizes hip bends. Taiji (Tai Chi) is a good candidate, and the Yang style of Taiji in particular.
If you were adventurous enough to try, you might consider Capoeira. It puts an emphasis on the torso and hips, putting them through a full range of motion probably more than any other martial art I've seen. But is it low impact? It can be, if you go slow and listen to your body. Does it put high loads on the lower back? It can, which is why you want to go slow to avoid accidentally loading the lower back. Capoeira is a slow and fast martial art, changing tempo as needed.
I think something like Capoeira would be good for younger people with sciatica, so long as they are in relatively good shape otherwise. It's not going to be for overweight, middle-aged people. The increased upper body weight you might have, combined with a lack of muscle tone, would make it much harder for you to keep your body under proper control in order to avoid impact and lower back loading.
Which leads me into the next point: Lose weight, improve muscle tone and strength. The biggest cause or contributor to sciatica pain is body fat weight. The extra weight puts a heavy load on your back, which can cause higher levels of sciatica pain. So you're going to have to drop that body fat if you want to see yourself improve. Secondly, by increasing muscle tone and strength, in particular around your core, it can hold your spine in place better, which can improve sciatica.
Another thing to consider would be yoga. It's not a martial art, but it can be used effectively for helping to treat sciatica.
Swimming is another thing to try.
And if you're taking up strength training, realize that you're going to have to focus on your core strength. But because of the fact that many exercises, such as the squat, put high load on the lower back, you should get a personal trainer or physical therapist who knows how to treat people with sciatica. Form is going to be your primary concern right now, and so you need to enlist the help of a really good personal trainer who understands correct form and can keep you from making painful mistakes.
Whatever you decide to do, always go slow and easy, and listen to your body. If it's making things worse, stop doing it.
Hope that helps.
Many (most?) martial arts are concerned primarily with fighting and/or sport, and health benefits are a side effect. With a condition like sciatica, I expect your primary motivation is health and not fighting.
Without any personal knowledge of sciatica, I would expect you would want to work on lower spinal mobility. In terms of yoga exercises, this would be moving between the cat and cow poses, rather than more static poses like downward dog. From the martial arts perspective, I think that taiji or bagua would expose you most to this motion in a martial context. Within taiji, I believe one of the Wu styles (sorry, don't know which) is known for a willowy spine motion, more so than the mostly upright Yang style. You can also search for Daoist (Taoist) spine stretch or Daoist spinal wave to see exercises that work this area. In a taiji context, I would want to find an instructor that works these kinds of exercises supplemental to forms training, rather than relying exclusively on forms training.