In reply to MaxDickson:
Pretty much what oceanrower says (though yeah, not soft, it should be surprisingly firm). Depends how much you want to spend, how you want to store it (taco style like being stored opened out) and how you'll going to transport it (i.e. will it fit in your car).
The UKC group test is a pretty handy guide: www.ukclimbing.com/gear/climbing/bouldering_mats/mid-sized_bouldering_mats-10017
Fwiw I have the moon warrior pad, which I'm very pleased with, but I've used a few and never been wildly unhappy.
Post edited at 23:02