Like Bose SoundSport Free with StayHear+ Sport tips, Apple also has their own signature eartips for Airpods Pro.
Just in case you lose Airpods Pro eartips.
You can contact support for a new pair. And it costs only $4 for replacements.
First off, Go to https://support.apple.com/ and then log in using your Apple ID, select: Replace an AirPod or Eartips and follow the step guide to get your new pair.
Currently I haven’t found aftermarket replacement tips for Airpods Pro yet. However they could arrive in the next few months.
These silicon eartips arrived earlier than I am expected. Available in black and while they are much cheaper than what Apple offer.
The most comfortable option, which is memory foam ear tips is also available (Ebay and Aliexpress). It’s not just about the comfort, the sound of your Airpods Pro will be slightly improved. You will feel more bass and “softer sound”.