Got a modern foam mattress as they were all the thing, a very well reviewed one, and regretted it ever since. It rapidly developed a sag under my quite moderate weight, and it keeps in heat rather well so in summer you cook. My advice is, don't. My next mattress will be the old fashioned sprung ones again. IME, YMMV.
In case anyone reads this:
One of the best things my wife and I have done in the past year was to switch to each of us having our own set of sheets. It's amazing. Highly recommended.
Do you have two twin mattresses side-by-side, each with its own set of sheets?
This is probably only feasible because we sleep on the floor, which means the blankets don't tend to wander in the night.
Lots of covers stealing other blanket shenanigans have been avoided in the past year though from that change.
Just launched a springy version at a 3x price-tag though!
Got the cheaper foamy one