What width is the strap on your watch
@Maddiecaddy ?
It could be a 168.010.
Lug width :
18mm = 168.004
19mm = 168.010
You can get a replacement crown for both ‘hidden crown’ Constellations that sits inside the crown recess, it still sticks out a little but will look better than the current crown you have on there and will be waterproof.
I would imagine finding a loose caseback - either for SS or gold cap will require equal patience - but first you need to determine the case reference.
If it is an .004 you will need to find a caseback from the same case manufacturer as they differ slightly. (Difficult to do if you don’t have the caseback to ascertain the manufacturer)
BTW IIRC gold cap cases are 14k not 18k.
As are the medallions on the caseback.