warranties and comfort guarantees are all reassuring, but are rendered irrelevant if you actually take the time to make sure you're getting the right mattress in the first place - here's a few tips:
the husband perspective - go to a showroom and sleep on the beds in succession. they are usually arranged by price so start with the cheapest and sleep your way up until you can't tell a comfort difference from the one before.
having basic criteria will make it easier to navigate a showroom - every retailer is going to have a different style name for your mattress model (googling mattress comparables on the the model your researching will help you price shop. i particularly like the mattressexpert.typepad.com). each retailer may carry only a few products wihin a particular line from each of the four major brands; basically there's the entry level line ($200 for a twin, $500 for a queen, $800 for a king not including delivery which is usually $100), and a midpriced range which you should aim for for about $200-$300 more, and a sucker/morbidly obese/chronic pain line...sound familiar? it should because that's what you'll get at ikea! at any retailer, make sure you aren't getting the impulse entry level model - it's usually the one advertised in the flyer and is only about $50-$100 less...they are perfect examples of why you can tell if you hate a mattress in under 5 minutes.
so why not ikea? because there's no thrill of the hunt. so if you have the energy and drive to save $100-$150, wait for a department store sale (and max out on coupons - and don't be afraid to ask what's going on sale...a lot of stores do pre-sale in advance!) or for the truly fearless, go to sleepy's with a competitor's price which they will match or beat at 20% less (again, research your comparables online!) or for the truly bold, just walk in and brazenly offer them about 50% off the tag price. the real trick is to not hvae buyer's remorse...yes there's always a chance that you could have saved an extra $100 but let it go...after sleeping on the perfect bed, you won't remember in a week!
additional peanut gallery advice: my husband is a light sleeper who prefers his side, i am a back/side sleeps-like-the-dead sleeper but will wake up more cranky if she doesn't get a good night's rest. so i'll let you decide who's the better half. to put it another way - it's the difference between sleeping on the beach and sleeping on a layer of feathers. we compromised by looking for a bed that feels like a layer of feathers on the beach. despite the imagery i'm sure this evokes, such things actually exist if you consider that most showroom models are 'broken in' and will arrive firmer than expected and most pillowtops will get smooshed down over time. can't tell? compare these pictures - the tighter woven cover even looks more rigid!
we needed a king mattress only (no box spring - raymour and flannigan and sleepy's allow for a $300 price drop, other stores like macy's can only order in sets. BEWARE not using a box spring will void the manufacturer's warranty). so not taking my father's advice about buying two twins (really, what does he know about making the bed convenience) because my husband and i tend to huddle together in the crack rather than sleep on opposite ends. some people opt for a split box spring which is essentially two twin box springs underneath your king mattress for easier removal, but it is about $100 more (also available for queen size but harder to find).
i grew up on mattresses that were practical and firm, slept on boarding school beds (get to school early so you can steal an extra stained 3" mattress) with a plank of wooden underneath, and paid my dues to those rubberizd monsters in college. i can also sleep standing up. my only back pain was from sitting on my fat ass, and went away with exercise. my husband has arthritis in his back from aggressive tennis playing (vis a vis an ambitious father...these were the michael chang years) and runs a little hot. combined we weigh about 300 pounds (you do the math, but just know pregnant i will outweigh him).
ruling out the tempurpedic (too hot), serta (the coils are not insulated so they make a racket and will bounce the other person), and stearns and foster (uses an imap system limits sales staff discretion with pricing). that left us with a simmons classic (entry level). so why didn't we go for the mid-range? because i'm cheap and the aestetic design differences (padded layer around circumference of mattress, grip handles) weren't worth the extra $300 - i mean, that's almost halfway towards another bed (and saves me the hassle of haggling a warranty).