So I then invested in a more expensive mat hoping it wouldn't crack up. It didn't crack. However, the wheels continue to make fairly deep impressions into the mat - not as bad as the carpet, but bad enough that it was a nuisance and I felt that I had to drag the chair out of the impressions just to move it.
Next, I invested in oversized casters, which made a big difference - until I rolled off the mat onto the carpet. Then I was back to square one.
I figured I need to come up with a better solution. I spent some time googling and found a few people saying they'd used furniture movers/sliders, but I couldn't find a step-by-step so I had to make up a few steps, but it worked out.
I hope it works for you.
Step 1: Create a Firm Foundation
They're perfect because they're round, solid and have a pre-drilled hole that comes in quite handy. The only challenge is that pre-drilled hole is filled with a lag screw that needs to be removed for our purposes. I found that channel lock pliers give the right leverage, but I'm sure vise grips would work equally well.
Simply unscrew and discard the lag screws.
Once I removed the lag screws, I replaced them with T-bolts, which I found in the specialty hardware section at Lowe's, and that fit perfect into the pre-drilled hole.
Step 2: Prepare Buns for Painting
As an added benefit, the screws came in quite handy to hold the buns while I painted them.
I also prepared fender washers, but ultimately didn't use them.
Step 3: Paint the Buns
Step 4: Prepare Star Base
First, you have to decide if you want to remove the base from the chair. I did, but it's not required. Regardless, remove the wheels/casters and flip the base/chair upside down.
My chair has decorative covers over the end of each leg that are held on with tiny screws, which are inserted through the holes used to insert the casters. I removed those screws easily using a manual screw driver.
Step 5: Drill Base to Receive Buns
The decorative covers on my chair were held by two screws - one in the wheel/caster holes, and the other a bit further up the leg.
When I drilled the first hole, it shattered the decorative cover on that leg. So for the next four, I taped the decorative cover with duct tape so it wouldn't have any give. That worked well for me.
Step 6: Install Buns
Remove the screws from the buns. Insert a screw through one of the newly drilled holes and screw the T-bolt onto the screw.
I found that I didn't need to use a screwdriver to hold the screw as I tightened the bun - which is nice, since it would have scratched the paint on the screw head.
After installing the remaining four buns, your star base will look like a UFO or hovercraft.
Step 7: Prepare Sliders
The type I purchased had foam inserts - supposedly to accommodate furniture legs - which needed to be removed. This took a bit of time but I needed a good surface for adhesion to the buns.
Step 8: Attach Sliders
I removed the backing paper on one strip and pressed it to the bottom of a bun. Then I pressed its "mate" onto it with the backing paper still intact. This ensures the two will be lined up perfect when installing the sliders. I used two pieces of 3M per bun.
After installing two 3M strips (with their mates) on each bun, remove the backing paper on the 3M strips on one of the buns. Carefully center one of the furniture sliders over the prepared bun and press down firmly to stick the 3M to the slider.
Repeat on the other four legs to complete the process.
Step 9: How Well Does It Work?
Now you've got 5 furniture sliders under your chair that will make it "float' on carpet. These sliders supposedly work on tile and hardwood, but I haven't tried it out.
Now that I don't sink into the carpet, I've removed my chair mat altogether.
I slide around the carpet quite easily. I wouldn't say it's like rolling on a hard surface, but it's definitely better than trying to get the wheels up out of a carpet rut.
Overall, I'm quite happy with the results.