I never buy thank you cards. Handmade thank you cards are easy to make and so much cheaper that I always just make a bunch of cards and keep them on hand. Plus, it adds an extra personal touch when you make a card yourself.
Punch out the hearts. I love the ombre look of the hearts.
Glue hearts onto card and use your alphabet stamps to stamp your sentiment.
You could also freehand your words or letters if you have good penmanship.
For the envelopes, I also add a heart paint chip cutout to tie the card together. There are millions of ways to punch out the paint chips and make cards. It’s great to do with kids and teach them to write thank you cards.