Sorry to hear about your problem: bed doesn't feel like it did in the showroom. This blog is the absolute best at learning about mattresses and toppers and what to do about it. Some of us here have many mattresses, toppers, and thousands of hours and dollars invested just trying to get a good nights sleep too, unfortunately, so you are at least in good... tired company.
For me, that is over 20 mattresses bought (many exchanges wheedled out of several suppliers), over $5k, 75 toppers, and thousands of hours pouring over this blog and another good one ccmattress.com, Peter Cancelli's blog from his NJ store. I am 170 lb M, side and back sleeper, 60, with lower back pain. I am not the best guide, because I am still searching for "better" but right now I am sleeping on 2 x 1 inch layers of soft latex on a really firm Serta bed.
1.Every mattress felt better in the showroom than after 8 or less hours at home.
2. Latex does not "soften up".. the whole point... if it "softened up" ... it would be 'breaking down." Good latex can last 20 years or more. My mother in law had one in the 50's that lasted 30 years. You need to buy "soft enough" and it will mostly stay that way, year after year.
3. Buy your toppers in 1 inch thicknesses and multiples. Two 1 inch are exactly like one 2 inch. When you buy a 1 inch queen, say, you can fold it over and feel what 2 inches feel like... with only a single layer bought. If you like 2 x 1 inches, (sleep overnight).. you are there. A lot of folks here don't trust a mattress underneath and go the route of eliminating the mattress and "build" their own mattress with a large block of either high density poly foam or latex.. and put 2-3 inches of softer latex (14-24 ILD) on top.
4. How firm you need is subjective. What ILD (indentation load deflection, a measure of "sink in") you will need will be a function of how heavy you are, body shape, sleep preference back or side, etc. Hard thing is that it is a blind purchase.
5. I have posted several comparisons of 1 inch toppers from two of the big suppliers, here's cliff notes:
www.Foambymail.com is cheapest Queen 20 ILD latex topper (their softest, start with that) is $98 shipping included. No return. I recommend starting with one of those.. you can see if 1 inch works, try 2 inches.. see if either of those works. If you need softer on the top layer ... most put softest latex on top and then firmer below that, if you need it, you will pay for it: www.sleeplikeabear.com sells a Queen 1 inch Talalay 14 ILD latex topper and claim it is the softest on the market. I have bought and tried both, using a FBM topper right now. When I tried the SLAB one, it came in a box half the size of the one from FBM, meaning it was indeed less dense, and would be perceived as softer. SLAB charges $172 shipped for Queen 1 inch. The good news is that SLAB will accept a refund with a restocking fee. I sent one back.. $32 from Atlanta, and at the time thought it was a bit softer but not enough to be worth double the price. I now wish I hadn't, and will probably order one this week. Both are good product. If you really need soft and don't want to risk "pretty soft"... the SLAB topper offers the chance to know.... and your exposure is $32.
6. Speaking from experience with bad back and combination side and back sleeper: you want as little soft layer as possible, so that your body almost "bottoms" out of the comfort layer, so there is resistance support, to be best for your back. I cannot use mem foam, because my body senses the sinking falling feeling and tries to hold my glutes up.. and I wake with huge back pains. Others like it. Same thing happens to me if my comfort layer of latex is too thick.
7. The search for the perfect bed or better bed will become an addiction. Jimsocal has posted 1,000 comments (thanks Jim! ... a wealth of information), has done major "mattress surgery".. and is still not satisfied! Scary to me. Others dive in... buy their latex stack, and pretty much hit it first time. So hoping tha
So welcome and good luck.