Needles & Grooves

I use a page called Sticker Ninja. Great selection of materials and they last a while too.

@swamp jazz box set has a good deal of experience with this, I think?

Quality wise, Rockin Monkey is great for stickers and they have a lot of cool finishes and textures for extra wow factor. If you want lowest price/deals, Sticker Mule does stickers and buttons and occasionally have deals online but I’m less excited about supporting their company as a first resort because of some of their CEO/owner’s political affiliations. But they’re good and cheap just as far as product goes.