I freehanded the envelope:

Basically I crocheted a square, ch 61, skip first chain and sc in each chain across, so I kept single crocheting the whole way until i was three quarters of the way through in completing the square. That’s when I started decreasing in one corner.
Sc2tog, sc in each stitch across, ch 1, turn.
Next row: sc in each stitch across and until last 2 stitches, sc2tog
Continue decreasing until the square shape is complete, then fold in corners to meet the curved shaped of bottom flap of envelope and sew together.

Made the heart and sewed it on as the seal.