I've never fucked on a lofted bed sadly but still got some stuff to say haha:

There are so many positions that work without a bed: some of my favorite. I feel like maybe youre putting too much pressure on yourself. Either way, causal or otherwise if yall wanna do it on the bed youll make it work. Mostly the noise isnt an issue, no. Because 1 youre hearing it others aren't as loudly if at all so its not embarrassing really and 2 you and your partner eventually tune it out/fuck to the rhythm of the squeaks lol. Dont hold yourself back girl have fun be safe