So I have a 2015 (June, Euro 5 Engine) 1.6TDI Skoda Octavia 105bhp (Estate/Combi)

I need to replace timing belt / water pump and have a mechanic that can do this. He quoted me £250 for timing belt kit but said I can buy myself if I like.

I have found this gates kit which says it fits my car - but, I'm unsure if I need switchable or non-switchable water pump? It says both fit and I'm unsure if that is correct?

These are the two -

non switchable: https://www.autodoc.co.uk/gates/13671357

switchable: https://www.autodoc.co.uk/gates/16612297

Please could you advise which one to order!

OE pumps are always switchable (with wire and moving collar around impeller wheel).

As aftermarket solutions (to be cheaper and/or avoid possible sticking of collar in future) non-switchable versions are available too- even from well-known brands.
Guys in Russian car forums installs non-switchable versions and says that those doesn't affect warm-up time dramatically

Have no personal experience with this but I would stick with switchable (like OE) version.

The links you have posted are for the Superb. The Octavia ones look to be different.