I also get to class twice a week. My studio has a great work/trade system, so I just help check in students at the start of class and do some dusting at the end and I get to attend for free! I think twice a week is enough for me. It's great for my flexibility, but it's also an intense muscle conditioning workout too.
Kind of off topic, but I also go to a meditation center once a week. It's not strictly exercise, but I think it helps with my weight loss by keeping my brain calm and collected through the week, no matter what my scale says.