For years I taught photographers how to create background photographing out of focus subjects in nature. Here is a link to a video on how to do that. 

https://youtu.be/MAxplsTZOsI

If you don't want to create your own backgrounds, don't have a printer, you can buy books of backgrounds at your local craft store.

I bought these two books at a Michael's Craft store.  They have books with solid colors, and books with pages of abstract patterns. Look in the aisle with paper backgrounds. Each book has 58 backgrounds.