Good replies!
protected.de looks like a winner with multiple options. Adhesive sleeves also seemed like easiest to use, thin and clear, but I need to check where the glue is before ordering. Thanks for bringing that up, didn't even think about it.
One of the worst CD packaging examples are those damn cardboard covers for Paysage D'Hiver! They came in a black envelopes but I threw away because they had no title or anything. I have them all and almost each one was already bent or bulking in a weird shape out the envelope. As if the cardboard had become wet, then dried up to its current shape. The material is also the kind that gets scuffed up very easily, and the size is not even any standard that would fit to DVD size protector. Argh...
I should also get some kind of closed storage box for LPs. The regular moving boxes can be piled up in two ways: handles in so you can put them on top of each other, or handles out, so the boxes slide into each other. The horror of a moving guy accidentally piling them incorrectly and smashing the records in below box could be real!
As I also buy a lot movies and have multiple Vinegar Syndrome releases. They sell also protective cases that fit for their slipcovers:
https://vinegarsyndrome.com/collections/cases Can be used with other labels that have the same standard size releases. A bit pricey, 3$ each, but those look nice on shelf. Buying import movies is expensive, and even so the prices for OOP releases, like Forgotten Gialli box for 100 €. I've started to get more covers for movies as well.
...then there's of course other collector enemies like UV light and DOGS. The kind of big dogs that do the weird head shake thing that sprays slime everywhere. It's something that I wasn't even thinking of until a I got a regular dog visitor in my household.