This is one of my favorite “romantic” DIY ideas. It’s cheap and super easy.
All you need are pictures of you and your significant other together, cute notes, balloons, string/ribbon, and tape.
Get a helium-filled balloon for each picture or note you want to hang. Either punch a hole on the note / picture and tie the string of the balloon through it, or tape the bottom of the string to the top of the picture or note. As long as the balloon is full enough of helium (which it should be), the pictures will hover slightly from the ground. Fill a room with these balloon notes and surprise your special someone by bringing them into the room. It’s a super romantic surprise!