A.L.
For yoga, I would recommend any classes specifically for pregnant women. Check with your delivering hospital for recommendations. They may have something on site.
As for other excerises, I attended my regular classes I attended and informed the instructor. If something doesn't feel good, don't do it. I just took it easier than normal. Walking is great if you can find an indoor track. I'm at week 27, and now am exclusively swimming. I'm not a great swimmer. I'm working with a swim coach every two weeks and using every implement there is (fins, noodle, ect). I get to the pool when it works for my schedule and it is costing me $5 each time. (Swim coach is separate). I'm located outside your range, but look for local clubs or YMCA.
Best of luck!