I'm not sure what you mean about the spiritual part since out of your post I would understand it's health and confidence related. Mostly all martial arts training increases self-confidence. I'd say the biggest boost in confidence is gained by training in something as close to reality as possible.
At least in my opinion you should choose a form of martial arts or a contact sport that deals with medium or full contact. The fact that you will receive moderate strikes during training will increase your mental toughness and will ensure that you will not be left in shock when being hit for real as it might happen if you never get hit during training. I witnessed what I have said above with people training Shotokan Karate as a competition sport and I'm sure it can happen to people from many other martial arts (not trying to blame Shotokan Karate for anything).
On the spiritual side I can't say that much but all martial arts develop discipline, character and the ability of detaching yourself from all other issues and focusing on the task at hand. Many teachers say "leave your problems at the Dojo's door". Furthermore, you can read a lot about health improvements from martial arts online. Starting from muscle build, flexibility, lung capacity due to cardio up to a stronger healthier back promoted by correct postures there are a lot of benefits.
Last but not least martial arts do not focus on strength in general. The role of the techniques is to use the maximum potential of your body against an opponent, in general against an opponent's weakest points or weaknesses.
Just look what's available in your area and then check out what seems best. Most important is to get a good teacher in any style. You could try Krav Maga or MMA if you want something real and complex just make sure the schools are good.