So I got this stand up rolling desk. I use it every day. It's not perfect, because my laptop is below eye level, but I think it's still better for me. And it was cheap and I could push it back into a hiding place when I'm done with it.
And it's worked out better than FitDesk Fitness Space Saving Semi Recumbent X Bike for Laptops, which, sadly was not easy to write on at all.
In a perfect world, I would have a treadmill desk. But we live in a teeny tiny house and there really isn't any place I could put one. Plus I was kind of bummed when I figured out you needed a way to mount your screen at eye level.