Hi johnbelushisgrandma and welcome to The Mattress Underground 
I’ve been tasked with picking out a mattress to replace our current, sagging one as we move across the country, and I’ve gotten a bit overwhelmed as I’ve started to go down various rabbit holes
Sorry to hear about your current sagging mattress. I can empathize with both you and your- girlfriend, a cross country move can be incredibly stressful, and finding a new mattress can be equally so!
First, you might read the Mattress Shopping Tutorial, as well as the Mattress Specifications You Need To Know and The Mattress Durability Guidelines. This will give you some tips and direction for you in your search. Any mattress is unique to those sleeping on it based on their Stats (height, BMI, sleeping position(s) and any underlying health conditions) and their PPP (Posture and alignment, Pressure relief, and Personal preferences).
and she isn’t interested in a DIY bed at this time. I compiled a spreadsheet of details about various mattresses from a couple of major review sites, but the information was conflicting (e.g., one site would say a mattress is good for side sleepers, and another would say it isn’t)
While a spreadsheet is a good idea, basing it on reviews is an exercise in frustration. As you have seen, these can be conflicting; there’s no way to tell if a review is ‘real’ or part of a marketing effort…and at the base point - those reviewers are not you, and their experience with any mattress can be completely opposite for the two of you. You don’t say what type of mattress your old sagging one is…and without Stats/PPP it would be impossible to make comments on most of the mattresses you listed. But there are a few general points that can be made.
We’re hoping to find a queen mattress that works for us in roughly the $1,000 range, though I may push to increase that budget slightly if it would make a big difference. Neither of us has tried a latex mattress or any of the Internet bed-in-a-box mattresses, though we are open to those kinds of suggestions. Since I move around a bit, I’m thinking typical memory foam is not the right fit, but I’m not ruling it out.
So far, I’m eyeing the following mattresses: Avocado Eco Organic, Leesa Legend (Costco), Ghostbed Luxe (Costco), Casper Select Hybrid (Costco), Brooklyn Bedding Aurora Luxe, Purple (basic model), and possibly the Nolah Evolution 15 or WinkBed, though the latter two are a little pricey and I haven’t found discounts yet. I’ve seen some conflicting info in reviews about the Avocado Eco Organic and Leesa Legend in particular. I do like the idea of an all-natural mattress from what I hope is an ethical company, but I don’t know if an all latex or latex hybrid mattress would be right for how we sleep. I’ve also been intrigued by how different Purple mattresses are, but their hybrids are a little too pricey for us.
Does any of these sound like a good fit for us? A quiet bed would also be preferable, but I don’t want to rule out coils if the right bed for us has them. I’ve also looked at Earthfoam/Sleep on Latex, but they haven’t been reviewed by the sites I’m using, and it sounds like we might need a thicker mattress as side sleepers
First, though you are both stressed out, if possible, you should take some time to go to a local retailer or showroom just to try different types of mattresses in person. You say you are own to latex but you have never tried it; latex is a great breathable material and is one of the most durable mattresses you can find…but not everyone likes the feel. Also, Talalay Latex and Dunlop Latex can have quite different ‘feels’ for many consumers. Memory foam can be great for reducing motion transfer - but excessive amounts of inexpensive low-density foam can wear out very quickly, causing ‘divots’ in areas which can cause pain and alignment issues. Hybrids as well can be great but you need to decide whether you enjoy the feel of an innerspring support layer…as you see there are many options out there just for the type of mattress, let alone different brands. This is why it’s so important to at least test some different types in person to get a ‘baseline’ of what you like and dislike, so you can focus on a manufacturer. Also, I agree a DIY can be a offer more flexibility is great but as it is you have quite a few new adventures on your hands and this endeavor it can take a LOT of ‘dialing in’ to find the right combination of comfort levels and layer placement, which might make you even more frustrated!
I would avoid the ‘bed in a box’ brands as well; though popular with many consumers these are highly compressed for ease of shipping and can sit in warehouses for an extended period which can cause west and damage to the mattress. Many of the mattresses you list don’t list all the specs you’d need to know so that you can make an educated decision of how durable the mattress would be as you don’t want to repeat the experience with a sagging mattress using a lower quality foam. This is why I recommend you read the tutorial and the mattress secs you need to know so that you can compare to the durability guidelines I linked above. I’d say this is your first priority of getting down a few basics to know what to look for in a mattress. All this being said, you do name GhostBed, who are Trusted Members of the site…these are all experienced mattress makers we have vetted for quality, transparency in their construction and components, and with a little information about your Stats, PPP, and mattress history, are well able to guide you to a comfortable mattress based on their experience with similar consumers.
It may seem like a lot, but don’t fall into ‘analysis paralysis’! A well thought out plan, with definite mattress types you consider to be comfortable, and types you don’t like, and a little more leg work, and you will be sure to find something that suits you both. If you want to provide you and your girlfriends Stats and PPP and a ‘shortlist’ of mattress types you are considering, we can certainly comment on them as to how they might work for you both.
Good luck with the moving prep, I hope it gets easier from here!
~ Basilio