I had the same problem. I took some laminate flooring, clicked a few together and laid that right on top of the carpet. Works great. I also put them in front of my long arm machine because I have a tall chair that I can use if my back goes out while I am long arm quilting. They do have a tendency to slide, but just slide them back every once in a while. Works like a charm.

If you get the right kind, they are designed to go over carpet. The kind of carpet you have matters. Some are designed for carpet only 1/4" thick while others go up to 3/4". Make sure you're matching the mat to the carpet.

The ones I've been buying are designed to go over carpet, they have the poky teeth on the bottom. Although I will admit I bought one once from IKEA that had no teeth - it was quite a bit cheaper and didn't last half as long. I haven't been able to locate any that would be considered a different grade, they all seem to be the same, made by the same company (except for that cheapo IKEA one).

I'll check out Costco's stock. If I end up buying one that will crack and break after a year or so, at least I'll end up paying less for it. I think I'll leave the plywood idea as a last resort - I also worry about rolling off of the edge and hurting myself!

Thanks for the replies, everyone!

In part the problem is the carpet pile. Higher pile allows the mat to flex. The more flexing the more likely to crack.

I worked for 19 years in the office supply business. There are mats out there with warranties. Don't recall brand names off the top of my head, but I know you can get them. They will be more expensive than the ones without a warranty, but definitely worth it.

You also need to check what pile depth the mat is designed for. If you have deep pile carpet and/or thick cushioning, your mat needs longer spikes to help prevent the cracking.
One of our customers was returning mats frequently and we determined that they had gotten a mat designed for low pile carpet (because it was less expensive) and the thick padding and deep pile carpet in their office was causing the mat to wear out more quickly than if they had gotten the one designed for the type of carpet they had.

ES Robbins is a brand available with specifications for the various thicknesses. Not sure about warranty on theirs, but they are a reputable company.

Just put carpet wheels on your chair rather than hard wood floor wheels. They work great and should solve the problem.

What's under your carpet? Is this room dedicated to your space or do you have to share it with guests?..
If it's your room and there's wood under there, pull up the carpet, either install the vinyl squares, or manufactored flooring. We installed wood, I've been pretty happy with it

Well this is an interesting idea, one that I didn't even know existed! Off to research what/where they are! Thank you!

Let us know what you find, I have never heard of them either!