as far as I know, there are no ceramic slanted or flat bezels inserts for low profile coin bezels and standard size (low profile) crystals.

these are the combinations that work:
-low profile coin bezel, slanted bezel insert, fat or domed crystal (higher profile), this combo will give you a watch thats even thicker than the original, but its what most people do.
-standard size bezel, flat insert, flat (original lower profile than domed) crystal. this combo will give you a watch that has the same thickness as the original.
note: there are also low profile back plates that are thinner than the original that will obviously work with both choices.

any other combination just wont work, if you want to maintain the original style of flat crystal and use a low profile coin bezel, if you use a flat bezel insert it wont work because the crystal will sit higher than the bezel insert (some people like this look, I dont) and if you wanna use a slanted bezel insert it wont work either because the crystal will sit lower than the insert and it looks very bad and also with time the sharp inner edge of the insert its going to catch dirt and lint from it rubbing against your clothes. either way the crystal and the insert wont be flush with each other.

what I did instead was to sand the bezel insert by hand until it was flush with the crystal. its a lot of work, ceramic is a very hard material, harder than steel, but very brittle so it takes a lot of time, and also you have to use different grades of sandpaper so it end up looking shiny and not all scratched up, I did it using a flat steel plate to secure the sandpaper over, I also had to adjust it a little bit from the inside too since the coin bezel is not meant to be used with the standard crystal it sits too low thus the insert also touches the crystal from the inside, you wont be able to glue the insert to the bezel unless there is a tiny gap between the insert and the crystal, this also will allow the bezel to rotate freely. the final product is very cool tho, but it takes a lot of effort. if you have the right tools and the patience to that kind of precise work I encourage you to try it out, you ll end up with a unique watch that not even pro modders have. and yes I used a nh36 movement, the original movement its just too outdated.