Nothing seems to be designed to last these days. There are lot of disposable single use items and even those that are supposed to last longer have limited time of uses before they start to show wear.
If you wish to keep them in pristine condition a while longer you need to protect them somehow. Luckily there are solutions on the market for that as well. Instead of buying new ones after they wear out you can try to protect your stuff with specially designed protective gear. Of course you need to do this from the beginning. No point of protecting those already a bit weared out items.
Which one then is more sustainable? Letting your stuff wear out and throw them away, or getting even more stuff to protect them and give them a bit longer lifespan.
Hard to say. It depends on how much, and long you keep using them. And not only you. With better condition it's possible to pass them on. Let somebody else enjoy of those things as well. If protecting the items in the first place means they can be used double the original time that's already worth protecting them. The protection probably doesn't come with equal strain than the item itself.