I 'm desperately trying to decorate this bottle but the glass paint I'm using doesn't seem to stay on...Could anyone give me advice on how to paint on glass and what would be easier to draw without causing complete chaos?

It might help to sand the bottle a bit with sandpaper, just to mar the surface enough to make paint stick. Acrylic paints tend to work on glass bottles from what I've seen. One of the local artists here paints wine bottles and I'm pretty sure she uses acrylics.

Maybe try painting bottles that are frosted or etched glass if you don't want to sand a smooth one.
Mosel Riesling comes in cat-shaped bottles and some of them are made of frosted glass. Funf wines come in green bottles that have already been painted white, so they're probably really easy to paint.