I sit in front of a computer hours and hours every day.

I eliminated my tendency to lean by buying chairs that have removable elbow rests. That also cleared up pain I was having in my shoulders because I was constantly pressing against the elbow rests and transferring pressure to my shoulders.

While a chair like you showed is really great for sitting, I don't think it's a great work chair if you're at the desk a good deal.

Also, define "expensive" in terms of chair costs?

The best, longest-lasting chair I ever had cost $800, and that was several years ago. It was worth every penny of that, considering how long it held up. That particular model is no longer made, or at least I couldn't find it anywhere. I bought something as close to it as I could for about $450. Both had memory foam.