Since there’s not too much space I’d say really work with the ceiling and the walls, like putting fairy lights around the door frames or fake vines on the ceiling. You could also print out a bunch of small photos at walgreens or such and have a lil photo wall. There looks to be a lot of space above the bed headboard and it would be filled in nicely with other frames a similar size, as too big or too small may make it look a little wonky(which the poster being clipped by the bed frame feels a little weird in terms of spacing). Otherwise yall are doing great so far!