Underrated mattress feature: motion separation. I think Simmons was the first to do it with their pocketed coils that don't transmit shocks laterally the way conventional mattresses do, but other brands probably offer something similar.

Absolutely essential if either of you is a light sleeper (my wife is) or have any tendency to toss and turn at night (I do.) Also good if your sleep schedules diverge, since one partner can read in bed and not worry as much about waking the other.