I have used water based paint (instead of oil based). It is much easier to clean up afterwards and does not smell as much. Depending on your wall, the roller is important.
Generally in CH, high gloss white paint is hard to find. White, in normal gloss and matt is available. I got all my paint from a Swiss paint producer/distributor. I searched on
www.search.ch for one close to me. There is one very close to glattzentrum in Zurich. I don't recall the name now, but can find it if you let me know. Generally if you discuss the price and are willing to pay cash, they will give you the handyman special (very close to the price they sell to professional painters).
I perfer not to buy paint from Swiss retailers, as I do not like to get Switzerlanded. Low end paint from Obi/Jumbo/Bauhaus is not quite the same and by the time I compared prices with mid/higher end paint, the price difference from the Swiss paint manufacturer/distributor was negligible.
When I bought my paint, I insisted that they put the containers in that machine and shake up the paint really well. I also bought one of those paint stirrers one can put in an electric drill and stir the paint.
All other necessary accessories (mask, covering, cleaning stuff, brushes, eye protection, paint holder, etc. etc) was much more economical in Obi/Jumbo/Bauhaus. I thought Co-op DIY was overpriced (at least in my area).