The best decodable books are the ones that follow your systematic scope and sequence. If you are looking for additional books to supplement your curriculum, here are some free and/or inexpensive ones I’ve found that are great choices:
Moon Dogs At Home – These books are free to print right now. They have excellent activity sheets that accompany them. Each book provides practice in multiple graphemes for one phoneme. (i.e. long /e/: ea, ee, ei, y) They do not look baby-ish and are a good choice for older readers.
These readers are offered in a PDF format from IMSE. They are reasonably priced, but you will have to print what you need. There are three different sets.
The CKLA curriculum offers free decodable readers for grades K-2. They must be printed, but are high quality. The link provided here will take you to my shared drive with readers for grades 1 and 2. A quick Google search will get you the books needed for K as well.
Emily Gibbons, The Literacy Nest, creates wonderful decodable passages, sentences, and word lists that are OG based. Her work is great and inexpensive, but would require printing.
Half Pint Kids offers readers you can purchase, but they also are available to read online for FREE.
These are not free, but they are reasonably priced. The storylines are great and the illustrations are awesome!
Beyond Decodables – These books are great (and FREE), but they are only about 80% decodable. The creator of the books states this on her site.
This company has decodable books that appeal to all ages. This is where the free Moon Dog Series comes from (see above). In addition to books, they also have a great selection of resources available for download (both free and paid).
The Sweet Science of Reading 