You should start by figuring out how many and what kinds of gyms are in your area. Once you know what the options are, it becomes much easier to make a choice. Some good arts to look for, off of the top of my head:
Sanda Kung Fu
Brazilian Jiu Jitsu
Any kind of wrestling (freestyle, greco roman, catch)
Once you know which, if any, of the gyms in your area teach those arts you can start checking them out. Talk to the instructors, figure out if it's in your price range, ask if you can take a trial class, ect. This probably won't be the case with any of the arts listed, but just as a heads up, if they demand that you sign a long-term contract, have child blackbelts, don't spar (or only do light contact/point sparring), don't want you to take a trial class or watch a class before signing up, ect, it's a red flag.
Whatever you pick, I'm sure that you'll do fine. Don't worry about cutting weight or trying to get in amazing shape while you're still a beginner. Just focus on finding somewhere to train, and if you have any questions after that you can always just ask the coach.
"I don't want them to like me, because when I'm in the ring, punches fly to the face. It is not a tenderness time. I am not falling in love. And he knows that when the fight starts I am kicking faces."
- Wanderlei Silva