I don't want to sound insulting but I just don't believe you. Let's say the bed is the larger double which is 4.5ft over the normal double of 4ft, that's just 2.25ft per adult. My should are wider than that. And those measurements are taking about being right on one edge of the bed to the other. I reality you want half a foot from the edge each side, so you're 2 adults sharing about 3.5ft.
A double is for a young adult, not 2 grown adults
Have you thought about getting a fan? Doesn't even need to be pointing at you, just some where in the room. I did this since I was 15 and pretty much have never slept without one since, even when I'm holidaying I take one with me. It cuts out almost all background noise, doors, cars, keys, shower etc you just struggle to hear them.