Thanks, yeah they are non slip. Yeah a laser level is a really good shout.
The fillet under the door might be a little annoying. I was originally thinking to have some rubber pads on the fillet and sit the tiles on that. Also allowing for proper drainage from the drainage holes in the frame. Although, looking at it more closely, I think I'll need to try to avoid having any strain on that fillet. Perhaps have some shallower pedestal to sit butted up against the fillet with some leveling underneath.