when i got my Octavia i only got one key, part of me is thinking having a second would be sensible.

My car is not remote locking if that matters. I noticed on ebay you can pick up a flip key, with remote, in my case redundant, functions. To be honest they look nicer, so could i have a key cut and programmed and get it to work? or do i need to stick to the style of key i have.

Related to this, can you actually retro-fit remote central locking?

You would probably need to code the key to the car immobilisor as well.

I guess it would need to be programmed to work with the immobiliser, but i don't know the ins and outs of doing so.

Have a look at the link in my signature it has some coding details.

You need to get a key that contains the correct type of transponder for immobiliser, you will also need to get the 4 digit PIN for your cars immobiliser.

Retro fitting factory remote locking would be very expensive (requiring a new convenience unit and naybe other parts as well as correct programming of these). An auto-electrician will probably be able to fit a (non Skoda) remote locking kit with a separate fob.