Hi Jenna,
There really is no way to compare innersprings and memory foam since innersprings are always used as a support core and memory foam is always used as a comfort layer so there is no way to do an “apples to apples” comparison. Memory foam comfort layers can use innersprings, high quality polyfoam, or latex foam as a support core (all of them can work well depending on the feel and qualities that are desired) while innerspring cores can use any material in a comfort layer above them (all of which except low density/quality polyfoam can work well depending on the feel and qualities desired).
There are no mattresses that use memory foam in the support layers (because memory foam is a non supportive foam and is unusitable for use there). There is a type of innerspring called microcoils that can be used in a comfort layer however but they are very different from the innersprings used in the support layers of a mattress and they are usually used in combination with some type of foam.
At Sleepy’s … the only mattress that I would consider to have real quality and better value would be the Pure Latex Bliss line. It comes in several models and there are two toppers that can be added to any of them so there is a wide range of choices available to customize the pressure relief, support, and feel to individual needs. While they are certainly high quality … mattresses that use the same materials and effective layering can be purchased for much less and since I have the “layer by layer” stats of these models … I would use them as a blueprint for a mattress that was purchased elsewhere rather than actually purchasing it (even though I would consider it to be the best value there). Stay away from the Dr Breus mattresses there which they will typically will tell you is a “latex mattress” when it only has some latex mixed in with lower quality materials (just check the law tag to verify this). They will often “steer” people who are looking for latex in this direction.
I would certainly stay away from any major brand such as the Serta iComfort as there are better options available using these as a “blueprint” as well that have significantly better value and quality. The last few posts in this thread may help you here as well in terms of higher value memory foam mattresses.
$3000 should be the “top of the line” in a budget IMO and can purchase a mattress that would likely cost 50% to 100% more at a major retailer. Very high quality and value can be purchased for significantly less than this even in a Split King, especially if they are using lower cost materials such as memory foam (lower cost compared to latex).
In terms of breathability and durability … latex will perform much better on both counts than memory foam. In terms of pressure relief … lower ILD latex (such as used in the PLB mattresses and toppers) have similar pressure relieving qualities to memory foam (osme say a little better some say a little worse but it would depend on the construction) and is much more supportive although they do “feel” different. The layer thickness, type of material, and the ILD (softness) of the materials used in the comfort layers are a critical part of how suitable a mattress may be for an individual. ILD is not as important in choosing memory foam as all memory foams would be conidered “very soft” in actual use and have a low ILD (typically 15 or less). Motion isolation between latex and memory foam would also be similar as their “point elasticity” is very similar (which is part of why they both relieve pressure so well). The biggest difference between the feel of latex and memory foam is that memory foam is much more “dead” feeling and doesn’t allow for easy movements in position while latex is more lively or buoyant and more towards an innerspring feel. Memory foam sleeps more “in” the mattress while latex sleeps more “on” the mattress.
While the mattress ticking/quilting and the materials used here can contribute a lot to the actual performance of a mattress, I certainly agree with you that the “look” of the ticking is far less important than how it actually contributes to the pressure relief and characteristics of the mattress.
Feather beds are great 
but they certainly need care and maintenance and will compress or break down over time … and there’s no doubt that you pay for quality here. While I haven’t done nearly as much research into featherbeds as I have other materials … there’s some good resources and information here about them.
Phoenix