Thicker mats?

[rydra_wong]

I've had an EcoYoga mat for ages and been pretty happy with it, but I'm considering getting a second, thicker mat now that I'm starting to work towards things like "floating" jumps and handstand (especially since my floors are hard wood and concrete).

Questions:

a) Is it worth it? Do the extra millimetres make a significant difference?

b) Got any recs for thicker mats? (Preferably ones available in the UK.)