If you've got a pair of Shure SE series or older E series headphones, you'll know that the foam sleeves provide the best combination of comfort and isolation. Depending on your hygiene standards, you'll also realise that they get collect earwax quite quickly, and lose their "sponginess" as more wax accumulates.
Just throw them in with your wash!
The solution? Well, you could buy some more, but have you tried washing them? Seriously, just put them in a zippable washing bag, and throw them in with your delicates cycle. They'll come out rejuvenated and will be good for a few more months. Of course, they'll still wear out eventually, but you'll get more use out of them than you would have without washing.
Remember, just wash the sleeves, not the headphones!