Being on the computer forces your shoulders forward and together. A split keyboard helps bring your shoulders back into a natural position. I recommend the Kinesis Freestyle 2, but there are quite a few alternatives on the market like the Ultimate Hacking Keyboard and KeyMouse.
There’s a lot of research about how sitting all day is harmful to your health. Treadmill desks are a really great way to combat this. The only one I’ve used is the Lifespan TR1200-DT3, which is one of the most popular and I’ve had a great experience with. Walking on the treadmill can be a little noisy. It’s generally not bad though and if it bothers you, you can always use a pair of Bose noise cancelling headphones.
Another way to combat sitting all day are sit-stand desks, which are becoming very popular. iMovr makes several made to be used with treadmills such as the iMovR Everest. It has a tilting keyboard tray, which does feel much more natural and is very steady when using a keyboard. The downside is that it isn’t quite wide enough to be used with a split keyboard like the Kinesis. The other downside is that the mouse doesn’t fit on the keyboard tray, so is placed on the desk. This means it’s higher than keyboard, which is unnatural and places extra strain on shoulder. A titled mousepad can help angle the mouse at the same angle as the keyboard and make it more comfortable to use. You can even stack two on top of each other to increase the angle.