I use this site for mail order. Good selection, good prices.
http://www.wallsandfl...category/floor-tiles/
If you're anywhere near Redruth, you could try here..........
http://www.varcurnmarble.co.uk/
If you're trying to keep well below £40/sq.m, then I guess glazed ceramic is the best option........... no sealing needed.
I wouldn't worry too much about durability. I would have thought a glazed tile was very durable. The only stone floor I've seen that does wear away over time, is bare terracotta.
What you choose is entirely subjective, Whatters ............. it's not something anyone can decide for you.
Don't despair! Just keep looking at as many as possible. :o)