Hi mannotbear.
Welcome to our Mattress Forum 
and good job narrowing down your choices! … the mattresses you selected use 8" pocket coil with added edge support you like and 3 zones for lumbar support and fall within your budget range. I’d say that you should opt for the most comfortable mattress with the highest density foams in the comfort layers (top 1/3) of the mattress. I’d want something with gel memory foam densities greater than 3.5lbs for a long-lasting mattress.
I’d pay special attention to the mattress “feel” you are looking for… especially in the comfort layer. Memory foam can be a “love it or hate it” material and it certainly has “weaknesses” that latex doesn’t have even though they are roughly equivalent in terms of cradling and their ability to relieve pressure. You can read more about the newer memory/poly foams. You can read more about the newer generation of polyfoams here that Aurora uses.
Helix uses only polyfoam and proprietary blends of memory foams in their products but depending on your firmness choice, Dusk would have a more in the mattress feel while with Luma’s you would get more on the mattress feel because of the resilience (springiness) of latex without losing the cradling effect. (This may also help with the pains and aches you mentioned because it’s inherent supportiveness and ease to reposition throughout the night) Aurora uses the new generation poly which has some of the latex properties.
Another thing I’d pay attention to is the breathability and how “hot the mattress sleeps”. Some types of memory foam are also more breathable than others and have less effect on sleeping temperature but memory foam, in general, tends to sleep warmer for some people than other types of foam materials (latex foam or polyfoam). There is more about the different properties that can be formulated into memory foam ~ post #9 here and post #8 here.
The price increase from Queen to King may be something to keep in mind if you have budgetary concerns … especially as you’d need to consider the foundation and all other sleeping accessories. As far as sagging goes … theoretically we have more space on the mattress to “wear out” but practically we’ll typically tend to drift towards the same spot on the mattress (weather Queen or King) which is where the most mechanical stress will occur. If the components used in the top layers of the mattress meet durability guidelines here you’d expect to have minimal impressions over time.
You may want Helix about the foam thickens they use in the comfort layers of their pillowtop of their Dusk Luxe, … site states 2.5 PCF density Visco Gel (IFD: 10.) // HD Memory Foam - IFD: Varies Density: 2.5 PCF Helix blend. // Dynamic Foam - latex-foam hybrid alternative: 10-20. Density: 3.0-4.0 PCF.
There is more about the 3 most important parts of the “value” of a mattress purchase in post #13 here helping with meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on suitability, durability, and all the other parts of your Mattress buying personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
I hope this gives a bit more info to help with your final choice.
Phoenix