I’d put a large, grounded ESD mat on your desk and then put your mousepad of choice on top of that. Consider an ESD floor mat. You can also get ESD sprays for surfaces and fabrics.
If you’re the arts and crafts type, you can buy woven nickel fabric (normally used for RFI shielding) and make your own mousepad, perhaps. I’ve used woven nickel adhesive tape to turn ordinary footwear into ESD footwear (which passed ESD testing).