I've been, I wore thermals and then skinny leather look jeans over the top and a jumper, and a duvet type coat. Hat and scarf and thermal gloves.
At the resort they give you the snowsuit and you really wouldn't be able to manage outside without it. They did have loads and loads of sizes and their were men with us with very big legs who were able to get suits so I would assume you would be OK.
One tip I have is that me and DS had our own snow boots and gloves which saved a lot of time queuing to get them, they are in lidl at the moment.
Also inside the grotto is really warm, I wish I'd had a layer under my jumper so I could have taken it off.
I can't remember if this was to do with us or in general (we went as a charity group for children with medical needs) but there was either nowhere to check your bag, the line was insane, or I needed the bag for DS's supplies and should have brought a smaller one with the bigger one.
But I remember being roasting hot, carrying a really heavy bag and being so flustered.
So in all.
Yes I think a snowsuit will fit
Maybe wear tracksuit bottoms or other trousers you are comfy in.
Bring a cooler layer for inside
Try and get your own boots and gloves to save time.
Bring a small bag - there must have been lockers or something I missed
Have an amazing time,!!! I always thought it was a complete racket but OMG it is so so so fantastic, magical and beautiful.