For my 4H girls, I enlarged a heart pattern and put a zipper in the side, starting at the point and going up. They then used a piece of ribbon at the top for a small bag. They all really liked that. If I were selling them, I would line them also. They were quick and easy.
A pillow with a felt "envelope" on the front that a love letter or gift card could be stuck in. The pillow would necessarily need to be made out of valentine fabric. Leave the pillow on the bed. When I leave a note it the envelope, I put the pillow on his side of the bed and vice versa. Something different.