Equimats - as above. Not cheap but fab stuuf, light, comfortable and durable. Company always helpfull if you need to amend something ie when moving stables. I have even put 'leftover' matting in outside pen and it lasts and lasts and lasts ...
I say Equimats too. Not a cheap option, but great quality & I can lift one on my own. Mine are 18mm thick & very comfy as they are 'veterinary' quality.
I sound like a sales person for this product but the truth is i can't recommend it highly enough.
NO TO MATS they are quite disgusting but a BIG YES to a COMPLETE covering of rubber. I have had this in 3 of my stables and wouldn't be without it, it is pricey but well worth it if you can stretch to it. The last 2 I had done a year ago and cost £1450 + VAT for a 12'6" x 14' and a 13'4" x 14'. It is called Solofloor by Kraiburg and will last for years and years, one complete sheet of thick rubber is sealed to the floor with an underlay and not one bit of mess or wee can get through, I love it and so do my old neddies, William Fox-Pitt has it you know!! This is there website www.kraiburg.co.uk if it helps.
Try these people, they are based in Balsall Common, the mats are reasonably priced, they don't charge a fortune to deliver & many at our stables have bought from them & been happy with them.
Equimats! Best mats ever in my opinion. Light, durable and when I lift mine yearly the disinfectant powder under them is still there, allow no moisture through.
Another vote for cow mats, lovely OH bought me 8 for my birthday and I think they came to around £450, I think the brand is called Quatro, they are incredibly tough (they have to put up with thousands of cloven hooves!) but lovely and light and easy to lift and clean under, plus they are thicker and more cushioned than your standard horse mats.