This is what we do. Most of our books ship just fine in the water-resistant bubble mailers from Sam’s. We keep a Sam’s membership mostly for our shipping supplies and get them in 2-3 sizes. If a book is a paperback that needs support to keep from bending, we throw in a piece or two of cardboard. We also keep one or two boxes on hand in case a book won’t fit in the bubble mailer, but we can get those almost anywhere, and we don’t use them often enough to worry too much about the cost of them. Especially since if we need a box, it is usually for something pricey enough to justify a higher cost to ship. Not always, but usually.
We stay away from Uline for the same reasons. My husband is in the process of folding the pages of the last catalogue they sent us so it will look like a Christmas tree . . . .