I have only ever owned Dunlopillo latex mattresses (Which? top mattress brand, btw). They last a very long time without any deterioration in support, but they are very pricey too.
I've recently bought a' Sealy 'Posturepaedic, from MattressOnline.co.uk and it's just the job. Check their site ,they do a great range with different support (at great prices). I've also used them for a 'standard' mattress for my son.