Here is an example of an entire thank you note for your reference:
Dear Aunt Katrina,
Thank you so much for letting me stay with you during my visit to New York. Seeing the city was such a wonderful experience for me, and it wouldn’t have been possible without your generous hospitality. Above all, it was so wonderful to spend some quality time with you and my sweet cousins. Let’s not let so much time pass before we get together again…how about a summer vacation my way? My home is always open to you and yours. Thanks again.