Martial arts are really hard to get into as a beginner. I'm physically fit and fairly flexible, but the dogmatism of many martial arts and the high barrier to entry (extreme strength and flexibility seem to be required even to start) made me really uncomfortable with a wide variety of martial arts. I've tried aikido, capoeira, kung fu muay-thai, boxing — but they all seemed to required beginners to immediately be able to do side-splits, acrobatic flips (I'm in NYC, so maybe the quality of beginners was much higher).

I'd recommend yoga in combination with weightlifting or HIIT training.