A Tilting Foot Rest is Ergonomically Correct

I noticed my feet were very sore at the end of my work day.  I was recently promoted and spend a lot more time at my desk on the computer.  A co-worker suggested that I order a height adjusting and tilting foot rest for under my desk.  It sounded like a good idea but I was not sure where to get one.  She gave me the website address of the company that she places work order through.  It was an ergonomic office supplies store.  I found a gray foot rest that looked like it would do the trick.  I am sure that my sitting position and posture plays a part into why I feel so tired at the end of the day.