Also, it's worth getting cups for the castor feet. Although it depends on the castors shape of course. But your sound like they are causing damage.
Not casters, they are feet. Never managed to find a suitable cup, though doubt they'd be much better, given the feet shape on the sofa. Which is probably why we can't find cups that fit

When we bought the underlay at the time, the indie fitter gave us choices, and I know this was the most expensive. Worth paying the extra IMHO. It is in as new condition, bar the 5 flattened bits under the larger of my sofas, and under "my" chair that has tolerated 14.5 stone for the last 13 years. I'm certainly not replacing the underlay in the rest of the house - even stairs etc, the underlay is untouched. I honestly believe this 13yr old would outlive the shite like Duralay Deluxe that shitfix sell.
To make matters more awkward, it has to be from a local supplier that will be open tomorrow or Monday. Carpets go in on Tues.