My lower arms often get sore after spending day after day scrolling with a mouse at work, and I use a similar product all the time! And I used to go to classes at my old gym that used balls very similar to these, and I cannot express both how much I miss the classes and how much they helped with the regular aches and pains that come from spending most of my days sitting at a desk. I still have a set of two balls from the class and pull them out every week or so!
But you don't *need* a class: there are lots of YouTube videos with good instructions so you can follow along! Here's a basic tutorial, a routine specifically for back pain, and one for hip pain. You can also do many of the exercises up against the wall, if they feel too intense on the floor. (Of course, if you're concerned about any of this, feel free to talk to your doctor first!)
Get them from Amazon Canada for $12.86 (available in four colours).