Sounds like a net pot which are quite often used to allow lots of air flow. Cattleyas like a lot of air flow which is probably the reason for the net pot.
My Cattleya is in bark not sure what others think is a good medium but as it likes it's roots to dry bark is likely to be better than moss (which stays wet a long time, especially in the UK climate).
I would advise getting a good quality medium if you are repotting, the stuff in garden centers can be already decayed. I use this website (link below) but there are other goods ones in the UK. Basically you want the stuff from an orchid specialist.
www.OrchidAccessories.com