Hi moseleymum, we brought a mattress last year from John Ryan By Design. They have a website full of information absolutely everything you could ever wish to know (or not know) about matresses and were really helpful on the phone. Our budget wouldn't stretch too far so we went for their pocket 1500 and one year later we are really pleased with it.
What I really liked was their guarantee that you can try it for a month, and they have lots of good reviews. They have to do this as I believe they only trade online so no chance to test their matresses. Felt more reassured by this than a quick try before you buy in John Lewis
Their customer service was really excellent and I would definitely use them again, they were one of those stand out companies you sadly don't come across too often.