I wouldn't spend 4k on a mattress. You can get a solid one for 1.5k tops. The important thing is doing the research beforehand, knowing what materials will last, and knowing what kind you prefer. After getting a couple of bad mattresses I got fed up and read up on it and was able to get a much better mattress because of it. Here's a site that seems to have a lot of good information. https://www.themattressunderground.com/our-articles/mattress...

We recently got a Saatva bed, and it is by far the best bed I've ever slept on. We had a Keetsa before that, and the Saatva completely blows it away. I think it was around $1500, money well spent.

Go to a Tempur-Pedic store and lie down on the mattresses. Feel them tenderly conform to your body shape. Toss and turn a little and feel them tenderly conform again.

I've tried all kinds of mattresses, from an IKEA latex mattress to a futon on the floor to a fancy Sealy hybrid-innerspring-memoryfoam. Tempur-Pedic is above and beyond. Yes, they're really expensive, but you spend a third of your life on your mattress and Tempur-Pedics last a long time.

My wife and I got a Keetsa four years ago and it is phenomenal--we get amazing sleep at less than half cost of Sam's mattress: https://shop.keetsa.com/collections/mattresses/products/tea-...

I would recommend stacking two foam mattresses from Ikea. Then try what works.

Spring constant is just spring constant no matter how much you spend money on it.