+1 for Tuft and Needle. I bought my king bed for $500 ($600 before promotional discounts) and I will probably never buy a mattress from any other company, ever again.
If you like a firm mattress (or feel as though you could get used to one--I did) Tuft and Needle mattresses are simple, inexpensive, durable and comfortable.
Just bought one from there for $600.
I chatted with their CSR for quite some time and she answered a lot of my questions. We both had some reservations about memory foam and it seems T&N doesn't have any of them.
Worst case we return it and try something else. Apparently only about 5% of people return them, though, according to the rep I talked with.