I'm getting an eco-stove fitted in my living room fireplace (replacing an open fireplace). I need to choose some tiles for the base, and will probably go for plain black (as seen lots of photos of stoves on plain black tiles). The advice from the fitter is "at least 12mm thick and suitable for inside a fireplace". How do I know if they're suitable or not? Can anyone suggest some they think would work well? Any recommended online suppliers? (I get decision anxiety about these things, so narrowing down what I need to filter on will help).