Hi ACfinder and welcome to the Mattress Underground 
I’m new here and a bit overwhelmed by information and possibilities. I received a $1000 gift from a family member to put towards a new mattress for my wife and me and am hoping you all can help narrow things down a bit.
I am a 5’7", ~210lb (33 BMI), side/back sleeper with minor hip and low back issues. My wife is a 5’3", 135lb (24 BMI), back sleeper.
What a great gift! Your being overwhelmed, as well as wanting the best value for your dollar is understandable. Keep in mind, any mattress you choose will be based on your Stats (height, BMI, sleeping position(s) and any underlying health conditions) - thanks for providing those! - and your PPP (Posture & alignment, Pressure relief, and Personal preferences).
My primary complaint is durability. Every mattress I’ve ever owned sags noticeably on my side within 6-12 months. My wife’s side holds up quite a bit better. I always assumed I preferred firm mattresses but I think I was confusing firmness with support and durability.
As far as durability is concerned…as you can see comparing the Mattress Specifications You Need To Know to the Mattress Durability Guidelines, latex is one of the most durable materials you can have in a mattress.
My wife prefers a marshmallow. Her favorite bed ever was at a vacation spot and consisted of what appeared to be a giant pillow layered over with thick quilts (think Princess and the Pea if you’ve ever read it)
My favorite was a brand new, decent quality, somewhat firm, inner spring mattress.
So the question is, can a durable custom queen-size latex or memory foam mattress with different firmness/support on either side be had for ~$1000-$1200? If so, where should I look?
The short answer is ‘yes!’ With caveats…first, no one - not here, not at a mattress showroom, not a manufacturer - can tell you which mattress will be best for you both, only you and your wife can determine that. As you are primarily thinking of durability, a latex mattress would be your best bet - if you both like the feel, of course, which not everyone does; also, keep in mind Talalay and Dunlop latex rubber have quite different ‘feels’, with Talalay being ‘bouncier’ (think of the difference between angel food cake vs. pound cake). If you go with memory foam, we suggest any foam in a potential mattress has no more than an inch or so of lower grade foams (for memory foam no lower than 4 lbs/cuft for normal range weights, and 5lbs/cuft for higher range weights) and if polyfoam is used, with at least 1.8 lbs/cuft density, just to ensure you have support. As you are a higher BMI sleeper, you want to make sure the foam density is provided so you can assess how it will support you.
A split-comfort layer mattress would provide you and your wife a more customized feel on your respective sides as you both have different preferences. With your lower back/hip issues you might want to, if possible, try out some foam and latex mattresses and hybrids at local showrooms if possible, so you can make a ‘short list‘ of mattress types you can further consider; then you can focus on finding the best value in your price range.
The Trusted Members of the site offer many different kinds of mattresses at a variety of price points, so depending on what type of mattress you are looking for, you should be able to find something in your budget. If you do see any specific mattress that catch your eye, feel free to post and we can possibly comment on the suitability and support, or if you decide what type of mattress seems to fit the bill, we can possibly also make some suggestions. Taking a little time and consideration will allow you to find your ideal sleep solution!
~ Basilio