Joining a gym. That was a thing we did.
It ended up being a pretty straightforward choice for us. The gym we joined has several classes we've been planning to pursue, a pool, and convenient locations and hours. When I did the math, the gym membership cost less than the classes and the community pool, as well as being more convenient than the latter, plus I can drop in before or after work and spend some time on the bikes or the weight machines.
I know there are lots of people who argue against joining a gym - it's an unnecessary expense, it's extra time, nobody ever goes, and so on. Believe me, I've thought through all of it. But the math for the classes Amber wants to take is pretty compelling, and paying some money to do a healthy thing versus paying no money to almost never to a healthy thing makes spending the money sound reasonable.
I've messed around with bodyweight exercise, with stuff you can do at home, with the paleo-style spontaneous exercise. But it comes back to the same thing everything else comes back to: I need habit. I need schedule. And I'm more effective when I acquiesce to that need rather than fighting it.
Since one of the gym locations is on my way home from work, I can easily go there two nights a week. Amber will meet me there after she gets back from work. Bam, instant schedule. Add in the Saturday morning tai chi class (yang style, I missed you!) and I have a workout plan that sounds sustainable, at least to me. Now I get to see how that works in practice, I suppose.