Hi Richard,

Can you be more specific with which brand and mattress name you are comparing? Depending on the make up, the Luxury Firm mattress may have a different coil gauge so it requires less foam than the Extra Firm. Also, details like how tightly the quilting is sewn down to the top of the bed will have an impact on the feel.

It's hard to tell with out know exactly which brand and mattress names you are comparing.

Hi Richard, Simply, one has nothing to do with the other.

Richard ditto on the above answers, but would strongly recommend you look for a 2 sided mattress so you can flip it over. The reason is 3- 3.5 inches of foam is a lot for an extra firm, all mattresses will soften with use and if you really like firm, the 2 sided design will and should give you a longer life in the mattress

Difference in height is accomplished a couple ways, primarily it is the amount of padding. And a two sided mattress will be taller, simply because the single sided does not have comfort materials on the bottom. The type of materials would be nice to know, which the retailer should be able to find out for you. Be careful about firmness, there is a limit to what firmness can do to ease pain. Buy the mattress that feels the best to you, not the hardest mattress. Take plenty of time lying on it before you commit to buy it, afterall you will probably have it for 8 to 10 years. My rule of thumb is to not buy a mattress until you have layed on it for at least 15 minutes, in your normal sleep position. It is also helpful to buy from a retailer who has a return policy, these policies differ widely, so know before you buy.

Visco foam is measured in density, the denser the material, the better it will react to your body heat and support the normal waking posture. Denser foam also should feel a bit firmer. But all foam comes in multiple quality levels, denser does not necessarily mean better.