Coil Count Is Critical - Any number above 390 in a queen size mattress should be plenty. In general, coils in all but the cheapest mattresses - less than $800 list price for a queen size - are "overdesigned for their function" and ought to provide years of service for most people.
Silk, Cashmere, and Wool Make A Bed More Comfortable - The small amounts usually used in the upper padding only make a bed more expensive. When you cover your mattress with a pad and sheets, you can't directly feel the surface anyway.
A Higher Price Guarantees A Better Bed - Anything but the cheapest mattresses can be a fine choice. Once you hit $800 or so for a queen size you should be fine in terms of quality.
If You Move In Your Sleep, The Bed Is To Blame - Turning is normal; it's a problem only if it disrupts your sleep. The mattress may or may not be at fault.
You Must Include The Boxspring To Save The Warranty - Despite sales pressure to buy both the mattress and the foundation, it is not always required. Check with the store or company - sometimes you may want to ask for a written record. If your old box spring is in good shape, you may be able to save $100-$200.
Stores Sell The Same Mattress Under Different Names - Retailers often claim that their mattress A is comparable to a competitor's mattress B. If you are comparing the same brand across retailers, this may be true. A Seally from one store may be name different from a similar Seally in another store. But don't let someone convince you that the Serta in one store has the exact same features as a Seally in another.
Salespeople Are Always Objective - Manufacturers dangle financial incentives known as SPIFs (for "sales person incentive funds") to push various brands and models. Commissions can amount to about $100 a bed.
Now that we've (hopefully) cleared up a few misconceptions, next we will go through how to choose your next mattress.