Welcome Heather! and Congratulations! I like to search “free wallpaper of…” The more imaginative the words you use, the better your results. And using “wallpaper” usually means the images will be higher resolution and beautiful for any size. Also you can look for “free stock images”. If you have any friends who are photographers, you can often get great original images for free (or low cost) and they’ll love that you use their art. There are several sites where you pay a monthly fee and can download a certain number of images per day. My sister did this (I forget which site) while building her website and collected hundreds of images for future use, cancelling when she was done. It wasn’t cheap but it gave her lots to work with and she’s still using them for brochures, articles, etc.