Tbh, if you're that paranoia about your phone, to the extent that you don't trust grapheneOS... Go back to a dumbphone.... The stuff you actually do on your phone (eg using anything on the internet through your provider/ISP) is probably 100x "riskier" than the insane offchance that some three letter agency is "hacking" your phone...

Pockets?

The only such case I found is this one but it looks a bit bulky: https://www.mobilefun.co.uk/olixar-stand-case-with-camera-privacy-cover-gold-for-google-6-pro-87401

But why not just use some painter's tape? The adhesive isn't very strong and usually doesn't leave residue when peeled off.

In addition to sliding cases for the back camera, there are also sticker slider add-ons for the front facing as well. You'll have to search based on your specific model, but be careful of the front facing sticker so they don't block the ambient light sensor on your device.

Painters tape

nillkin makes cases with camera covers.

Yes! Here is but one example: https://amzn.eu/d/3PPodHU

I searched for, "phone camera shutter privacy".

The solution you're looking for is called "black electrical tape".

It's simple, easy to use, comes off easy, and can be found at any hardware store.

For the front facing camera you can buy stickers or a little stick on shutter that you can flip open and closed. You could maybe do the same with the back but that may involve covering the flash as well.

ZUCUCUC Laptop Camera Cover Slide, Phone 6 Pack Ultra Thin Webcam Slide for Laptop, Desktop, PC, Tablet, Smartphone, Protect Your Privacy and Security(Black) https://a.co/d/4cYj4U4

You could remove the glass over the lenses and physically break the cameras then put the glass back on