I've a big collection of bookmarks!
Always use them!
To turn down a book page is anathema to me!
If I get a Library book, & this has happened, I press the crease, to try & eradicate it.
When working, used to carry 'spares' with me, in my briefcase, & if I saw someone close by,
about to page turndown, I'd give them one of my spares, such is my hate of that action, to a book!
I was taught by my Parents' to respect books, so it is to this day that I do, & will forever.
If I have a big collection of spares, I give them to my local Library, as they give them to less fortunate folk, who are house-bound.
I often see a 'card' that's beautiful, so I buy it as a bookmark, & keep it in its' cellophane cover, to stay clean!
At the moment, my bookmark is the 'label' from 'on hold' book from Library! Probably the simplest I've used for ages!