My grandfather was a sailor, and during his travels, he collected patches from every port he visited. Like your water bottle, his duffle bag served as his worldly canvas. After years of journeys and countless patches, he faced a similar problem as you. How could he protect the pathes without compromising on the bag's functionality and charm?

Ngl his solution was kinda genius. Rather than using a sealant which might affect the texture and appearance of his bag, he opted for clear, thin, waterproof vinyl cover. He carefully sewed it onto the ba and basically created a protective layer that was hardly visible. It maintained the bag's flexibility, and all the patches were well protected from wear and tear.

Thinking about your situation, perhaps a similar solution could work. If applied correctly a thin layer of clear, protective, flexible vinyl could safeguard your precious stickers while keeping your bottle usable. You'd have to ensure it adheres perfectly to the curved surface, but I believe the effort would be worth it.

I'm sure there are industrial strength adhesives safe for use which could affix the vinyl layer perfectly